Add synchronization with gPodder Nextcloud server app (#5243)

41 files changed, 1526 insertions, 764 deletions

diff --git a/app/src/main/java/de/danoeh/antennapod/activity/PreferenceActivity.java b/app/src/main/java/de/danoeh/antennapod/activity/PreferenceActivity.java
index 600204554..1fc16ab32 100644
--- a/app/src/main/java/de/danoeh/antennapod/activity/PreferenceActivity.java
+++ b/app/src/main/java/de/danoeh/antennapod/activity/PreferenceActivity.java
@@ -6,6 +6,7 @@ import android.os.Bundle;
 import android.provider.Settings;
 import android.view.Menu;
 import android.view.MenuItem;
+
 import android.view.View;
 import android.view.inputmethod.InputMethodManager;
 
@@ -21,13 +22,13 @@ import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.databinding.SettingsActivityBinding;
 import de.danoeh.antennapod.fragment.preferences.AutoDownloadPreferencesFragment;
-import de.danoeh.antennapod.fragment.preferences.GpodderPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.ImportExportPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.MainPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.NetworkPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.NotificationPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.PlaybackPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.StoragePreferencesFragment;
+import de.danoeh.antennapod.fragment.preferences.synchronization.SynchronizationPreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.SwipePreferencesFragment;
 import de.danoeh.antennapod.fragment.preferences.UserInterfacePreferencesFragment;
 
@@ -76,8 +77,8 @@ public class PreferenceActivity extends AppCompatActivity implements SearchPrefe
             prefFragment = new ImportExportPreferencesFragment();
         } else if (screen == R.xml.preferences_autodownload) {
             prefFragment = new AutoDownloadPreferencesFragment();
-        } else if (screen == R.xml.preferences_gpodder) {
-            prefFragment = new GpodderPreferencesFragment();
+        } else if (screen == R.xml.preferences_synchronization) {
+            prefFragment = new SynchronizationPreferencesFragment();
         } else if (screen == R.xml.preferences_playback) {
             prefFragment = new PlaybackPreferencesFragment();
         } else if (screen == R.xml.preferences_notifications) {
@@ -101,8 +102,8 @@ public class PreferenceActivity extends AppCompatActivity implements SearchPrefe
             return R.string.import_export_pref;
         } else if (preferences == R.xml.preferences_user_interface) {
             return R.string.user_interface_label;
-        } else if (preferences == R.xml.preferences_gpodder) {
-            return R.string.gpodnet_main_label;
+        } else if (preferences == R.xml.preferences_synchronization) {
+            return R.string.synchronization_pref;
         } else if (preferences == R.xml.preferences_notifications) {
             return R.string.notification_pref_fragment;
         } else if (preferences == R.xml.feed_settings) {
diff --git a/app/src/main/java/de/danoeh/antennapod/discovery/GpodnetPodcastSearcher.java b/app/src/main/java/de/danoeh/antennapod/discovery/GpodnetPodcastSearcher.java
index f97c1c7ab..340783208 100644
--- a/app/src/main/java/de/danoeh/antennapod/discovery/GpodnetPodcastSearcher.java
+++ b/app/src/main/java/de/danoeh/antennapod/discovery/GpodnetPodcastSearcher.java
@@ -1,6 +1,6 @@
 package de.danoeh.antennapod.discovery;
 
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
 import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetServiceException;
@@ -18,8 +18,8 @@ public class GpodnetPodcastSearcher implements PodcastSearcher {
         return Single.create((SingleOnSubscribe<List<PodcastSearchResult>>) subscriber -> {
             try {
                 GpodnetService service = new GpodnetService(AntennapodHttpClient.getHttpClient(),
-                        GpodnetPreferences.getHosturl(), GpodnetPreferences.getDeviceID(),
-                        GpodnetPreferences.getUsername(), GpodnetPreferences.getPassword());
+                        SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getDeviceID(),
+                        SynchronizationCredentials.getUsername(), SynchronizationCredentials.getPassword());
                 List<GpodnetPodcast> gpodnetPodcasts = service.searchPodcasts(query, 0);
                 List<PodcastSearchResult> results = new ArrayList<>();
                 for (GpodnetPodcast podcast : gpodnetPodcasts) {
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/PodcastListFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/PodcastListFragment.java
index c813cbf7a..af502ce13 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/PodcastListFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/PodcastListFragment.java
@@ -15,7 +15,7 @@ import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.activity.MainActivity;
 import de.danoeh.antennapod.activity.OnlineFeedViewActivity;
 import de.danoeh.antennapod.adapter.gpodnet.PodcastListAdapter;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
 import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetServiceException;
@@ -76,8 +76,8 @@ public abstract class PodcastListFragment extends Fragment {
         disposable = Observable.fromCallable(
                 () -> {
                     GpodnetService service = new GpodnetService(AntennapodHttpClient.getHttpClient(),
-                            GpodnetPreferences.getHosturl(), GpodnetPreferences.getDeviceID(),
-                            GpodnetPreferences.getUsername(), GpodnetPreferences.getPassword());
+                            SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getDeviceID(),
+                            SynchronizationCredentials.getUsername(), SynchronizationCredentials.getPassword());
                     return loadPodcastData(service);
                 })
                 .subscribeOn(Schedulers.io())
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/TagListFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/TagListFragment.java
index f961e30bb..abdfab941 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/TagListFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/gpodnet/TagListFragment.java
@@ -8,7 +8,7 @@ import androidx.annotation.NonNull;
 import androidx.fragment.app.ListFragment;
 import de.danoeh.antennapod.activity.MainActivity;
 import de.danoeh.antennapod.adapter.gpodnet.TagListAdapter;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
 import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
 import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetTag;
@@ -51,8 +51,8 @@ public class TagListFragment extends ListFragment {
         disposable = Observable.fromCallable(
             () -> {
                 GpodnetService service = new GpodnetService(AntennapodHttpClient.getHttpClient(),
-                        GpodnetPreferences.getHosturl(), GpodnetPreferences.getDeviceID(),
-                        GpodnetPreferences.getUsername(), GpodnetPreferences.getPassword());
+                        SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getDeviceID(),
+                        SynchronizationCredentials.getUsername(), SynchronizationCredentials.getPassword());
                 return service.getTopTags(COUNT);
             })
                 .subscribeOn(Schedulers.io())
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/GpodderPreferencesFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/GpodderPreferencesFragment.java
deleted file mode 100644
index 4fb734e17..000000000
--- a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/GpodderPreferencesFragment.java
+++ /dev/null
@@ -1,128 +0,0 @@
-package de.danoeh.antennapod.fragment.preferences;
-
-import android.app.Activity;
-import android.os.Bundle;
-import androidx.core.text.HtmlCompat;
-import androidx.preference.PreferenceFragmentCompat;
-
-import android.text.Spanned;
-import android.text.format.DateUtils;
-import com.google.android.material.snackbar.Snackbar;
-import de.danoeh.antennapod.R;
-import de.danoeh.antennapod.activity.PreferenceActivity;
-import de.danoeh.antennapod.core.event.SyncServiceEvent;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
-import de.danoeh.antennapod.core.sync.SyncService;
-import de.danoeh.antennapod.dialog.AuthenticationDialog;
-import org.greenrobot.eventbus.EventBus;
-import org.greenrobot.eventbus.Subscribe;
-import org.greenrobot.eventbus.ThreadMode;
-
-public class GpodderPreferencesFragment extends PreferenceFragmentCompat {
-    private static final String PREF_GPODNET_LOGIN = "pref_gpodnet_authenticate";
-    private static final String PREF_GPODNET_SETLOGIN_INFORMATION = "pref_gpodnet_setlogin_information";
-    private static final String PREF_GPODNET_SYNC = "pref_gpodnet_sync";
-    private static final String PREF_GPODNET_FORCE_FULL_SYNC = "pref_gpodnet_force_full_sync";
-    private static final String PREF_GPODNET_LOGOUT = "pref_gpodnet_logout";
-
-    @Override
-    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
-        addPreferencesFromResource(R.xml.preferences_gpodder);
-        setupGpodderScreen();
-    }
-
-    @Override
-    public void onStart() {
-        super.onStart();
-        ((PreferenceActivity) getActivity()).getSupportActionBar().setTitle(R.string.gpodnet_main_label);
-        updateGpodnetPreferenceScreen();
-        EventBus.getDefault().register(this);
-    }
-
-    @Override
-    public void onStop() {
-        super.onStop();
-        EventBus.getDefault().unregister(this);
-        ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle("");
-    }
-
-    @Subscribe(threadMode = ThreadMode.MAIN, sticky = true)
-    public void syncStatusChanged(SyncServiceEvent event) {
-        updateGpodnetPreferenceScreen();
-        if (!GpodnetPreferences.loggedIn()) {
-            return;
-        }
-        if (event.getMessageResId() == R.string.sync_status_error
-                || event.getMessageResId() == R.string.sync_status_success) {
-            updateLastGpodnetSyncReport(SyncService.isLastSyncSuccessful(getContext()),
-                    SyncService.getLastSyncAttempt(getContext()));
-        } else {
-            ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle(event.getMessageResId());
-        }
-    }
-
-    private void setupGpodderScreen() {
-        final Activity activity = getActivity();
-
-        findPreference(PREF_GPODNET_LOGIN).setOnPreferenceClickListener(preference -> {
-            new GpodderAuthenticationFragment().show(getChildFragmentManager(), GpodderAuthenticationFragment.TAG);
-            return true;
-        });
-        findPreference(PREF_GPODNET_SETLOGIN_INFORMATION)
-                .setOnPreferenceClickListener(preference -> {
-                    AuthenticationDialog dialog = new AuthenticationDialog(activity,
-                            R.string.pref_gpodnet_setlogin_information_title, false, GpodnetPreferences.getUsername(),
-                            null) {
-
-                        @Override
-                        protected void onConfirmed(String username, String password) {
-                            GpodnetPreferences.setPassword(password);
-                        }
-                    };
-                    dialog.show();
-                    return true;
-                });
-        findPreference(PREF_GPODNET_SYNC).setOnPreferenceClickListener(preference -> {
-            SyncService.syncImmediately(getActivity().getApplicationContext());
-            return true;
-        });
-        findPreference(PREF_GPODNET_FORCE_FULL_SYNC).setOnPreferenceClickListener(preference -> {
-            SyncService.fullSync(getContext());
-            return true;
-        });
-        findPreference(PREF_GPODNET_LOGOUT).setOnPreferenceClickListener(preference -> {
-            GpodnetPreferences.logout();
-            Snackbar.make(getView(), R.string.pref_gpodnet_logout_toast, Snackbar.LENGTH_LONG).show();
-            updateGpodnetPreferenceScreen();
-            return true;
-        });
-    }
-
-    private void updateGpodnetPreferenceScreen() {
-        final boolean loggedIn = GpodnetPreferences.loggedIn();
-        findPreference(PREF_GPODNET_LOGIN).setEnabled(!loggedIn);
-        findPreference(PREF_GPODNET_SETLOGIN_INFORMATION).setEnabled(loggedIn);
-        findPreference(PREF_GPODNET_SYNC).setEnabled(loggedIn);
-        findPreference(PREF_GPODNET_FORCE_FULL_SYNC).setEnabled(loggedIn);
-        findPreference(PREF_GPODNET_LOGOUT).setEnabled(loggedIn);
-        if (loggedIn) {
-            String format = getActivity().getString(R.string.pref_gpodnet_login_status);
-            String summary = String.format(format, GpodnetPreferences.getUsername(),
-                    GpodnetPreferences.getDeviceID());
-            Spanned formattedSummary = HtmlCompat.fromHtml(summary, HtmlCompat.FROM_HTML_MODE_LEGACY);
-            findPreference(PREF_GPODNET_LOGOUT).setSummary(formattedSummary);
-            updateLastGpodnetSyncReport(SyncService.isLastSyncSuccessful(getContext()),
-                    SyncService.getLastSyncAttempt(getContext()));
-        } else {
-            findPreference(PREF_GPODNET_LOGOUT).setSummary(null);
-        }
-    }
-
-    private void updateLastGpodnetSyncReport(boolean successful, long lastTime) {
-        String status = String.format("%1$s (%2$s)", getString(successful
-                        ? R.string.gpodnetsync_pref_report_successful : R.string.gpodnetsync_pref_report_failed),
-                        DateUtils.getRelativeDateTimeString(getContext(),
-                        lastTime, DateUtils.MINUTE_IN_MILLIS, DateUtils.WEEK_IN_MILLIS, DateUtils.FORMAT_SHOW_TIME));
-        ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle(status);
-    }
-}
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/MainPreferencesFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/MainPreferencesFragment.java
index cc09acbca..83ad3110a 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/MainPreferencesFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/MainPreferencesFragment.java
@@ -17,12 +17,11 @@ import de.danoeh.antennapod.core.util.IntentUtils;
 import de.danoeh.antennapod.fragment.preferences.about.AboutFragment;
 
 public class MainPreferencesFragment extends PreferenceFragmentCompat {
-    private static final String TAG = "MainPreferencesFragment";
 
     private static final String PREF_SCREEN_USER_INTERFACE = "prefScreenInterface";
     private static final String PREF_SCREEN_PLAYBACK = "prefScreenPlayback";
     private static final String PREF_SCREEN_NETWORK = "prefScreenNetwork";
-    private static final String PREF_SCREEN_GPODDER = "prefScreenGpodder";
+    private static final String PREF_SCREEN_SYNCHRONIZATION = "prefScreenSynchronization";
     private static final String PREF_SCREEN_STORAGE = "prefScreenStorage";
     private static final String PREF_DOCUMENTATION = "prefDocumentation";
     private static final String PREF_VIEW_FORUM = "prefViewForum";
@@ -74,8 +73,8 @@ public class MainPreferencesFragment extends PreferenceFragmentCompat {
             ((PreferenceActivity) getActivity()).openScreen(R.xml.preferences_network);
             return true;
         });
-        findPreference(PREF_SCREEN_GPODDER).setOnPreferenceClickListener(preference -> {
-            ((PreferenceActivity) getActivity()).openScreen(R.xml.preferences_gpodder);
+        findPreference(PREF_SCREEN_SYNCHRONIZATION).setOnPreferenceClickListener(preference -> {
+            ((PreferenceActivity) getActivity()).openScreen(R.xml.preferences_synchronization);
             return true;
         });
         findPreference(PREF_SCREEN_STORAGE).setOnPreferenceClickListener(preference -> {
@@ -142,8 +141,8 @@ public class MainPreferencesFragment extends PreferenceFragmentCompat {
                 .addBreadcrumb(PreferenceActivity.getTitleOfPage(R.xml.preferences_network))
                 .addBreadcrumb(R.string.automation)
                 .addBreadcrumb(PreferenceActivity.getTitleOfPage(R.xml.preferences_autodownload));
-        config.index(R.xml.preferences_gpodder)
-                .addBreadcrumb(PreferenceActivity.getTitleOfPage(R.xml.preferences_gpodder));
+        config.index(R.xml.preferences_synchronization)
+                .addBreadcrumb(PreferenceActivity.getTitleOfPage(R.xml.preferences_synchronization));
         config.index(R.xml.preferences_notifications)
                 .addBreadcrumb(PreferenceActivity.getTitleOfPage(R.xml.preferences_notifications));
         config.index(R.xml.feed_settings)
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/NotificationPreferencesFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/NotificationPreferencesFragment.java
index 94e151f7a..ba17cedb2 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/NotificationPreferencesFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/NotificationPreferencesFragment.java
@@ -4,11 +4,10 @@ import android.os.Bundle;
 import androidx.preference.PreferenceFragmentCompat;
 import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.activity.PreferenceActivity;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
 
 public class NotificationPreferencesFragment extends PreferenceFragmentCompat {
 
-    private static final String TAG = "NotificationPrefFragment";
     private static final String PREF_GPODNET_NOTIFICATIONS = "pref_gpodnet_notifications";
 
     @Override
@@ -24,7 +23,6 @@ public class NotificationPreferencesFragment extends PreferenceFragmentCompat {
     }
 
     private void setUpScreen() {
-        final boolean loggedIn = GpodnetPreferences.loggedIn();
-        findPreference(PREF_GPODNET_NOTIFICATIONS).setEnabled(loggedIn);
+        findPreference(PREF_GPODNET_NOTIFICATIONS).setEnabled(SynchronizationSettings.isProviderConnected());
     }
 }
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/GpodderAuthenticationFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/GpodderAuthenticationFragment.java
index c0bf3e0ea..9dfe6840c 100644
--- a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/GpodderAuthenticationFragment.java
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/GpodderAuthenticationFragment.java
@@ -1,4 +1,4 @@
-package de.danoeh.antennapod.fragment.preferences;
+package de.danoeh.antennapod.fragment.preferences.synchronization;
 
 import android.app.Dialog;
 import android.content.Context;
@@ -15,30 +15,35 @@ import android.widget.ProgressBar;
 import android.widget.RadioGroup;
 import android.widget.TextView;
 import android.widget.ViewFlipper;
+
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AlertDialog;
 import androidx.fragment.app.DialogFragment;
+
 import com.google.android.material.button.MaterialButton;
 import com.google.android.material.textfield.TextInputLayout;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
 import de.danoeh.antennapod.R;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
 import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
 import de.danoeh.antennapod.core.sync.SyncService;
-import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetDevice;
+import de.danoeh.antennapod.core.sync.SynchronizationProviderViewData;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
 import de.danoeh.antennapod.core.util.FileNameGenerator;
 import de.danoeh.antennapod.core.util.IntentUtils;
+import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetDevice;
 import io.reactivex.Completable;
 import io.reactivex.Observable;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.schedulers.Schedulers;
 
-import java.util.List;
-import java.util.Locale;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
-
 /**
  * Guides the user through the authentication process.
  */
@@ -83,23 +88,24 @@ public class GpodderAuthenticationFragment extends DialogFragment {
         final RadioGroup serverRadioGroup = view.findViewById(R.id.serverRadioGroup);
         final EditText serverUrlText = view.findViewById(R.id.serverUrlText);
 
-        if (!GpodnetService.DEFAULT_BASE_HOST.equals(GpodnetPreferences.getHosturl())) {
-            serverUrlText.setText(GpodnetPreferences.getHosturl());
+        if (!GpodnetService.DEFAULT_BASE_HOST.equals(SynchronizationCredentials.getHosturl())) {
+            serverUrlText.setText(SynchronizationCredentials.getHosturl());
         }
         final TextInputLayout serverUrlTextInput = view.findViewById(R.id.serverUrlTextInput);
         serverRadioGroup.setOnCheckedChangeListener((group, checkedId) -> {
             serverUrlTextInput.setVisibility(checkedId == R.id.customServerRadio ? View.VISIBLE : View.GONE);
         });
         selectHost.setOnClickListener(v -> {
+            SynchronizationCredentials.clear(getContext());
             if (serverRadioGroup.getCheckedRadioButtonId() == R.id.customServerRadio) {
-                GpodnetPreferences.setHosturl(serverUrlText.getText().toString());
+                SynchronizationCredentials.setHosturl(serverUrlText.getText().toString());
             } else {
-                GpodnetPreferences.setHosturl(GpodnetService.DEFAULT_BASE_HOST);
+                SynchronizationCredentials.setHosturl(GpodnetService.DEFAULT_BASE_HOST);
             }
             service = new GpodnetService(AntennapodHttpClient.getHttpClient(),
-                    GpodnetPreferences.getHosturl(), GpodnetPreferences.getDeviceID(),
-                    GpodnetPreferences.getUsername(), GpodnetPreferences.getPassword());
-            getDialog().setTitle(GpodnetPreferences.getHosturl());
+                    SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getDeviceID(),
+                    SynchronizationCredentials.getUsername(), SynchronizationCredentials.getPassword());
+            getDialog().setTitle(SynchronizationCredentials.getHosturl());
             advance();
         });
     }
@@ -116,7 +122,7 @@ public class GpodderAuthenticationFragment extends DialogFragment {
         createAccount.setPaintFlags(createAccount.getPaintFlags() | Paint.UNDERLINE_TEXT_FLAG);
         createAccount.setOnClickListener(v -> IntentUtils.openInBrowser(getContext(), "https://gpodder.net/register/"));
 
-        if (GpodnetPreferences.getHosturl().startsWith("http://")) {
+        if (SynchronizationCredentials.getHosturl().startsWith("http://")) {
             createAccountWarning.setVisibility(View.VISIBLE);
         }
         password.setOnEditorActionListener((v, actionID, event) ->
@@ -265,15 +271,8 @@ public class GpodderAuthenticationFragment extends DialogFragment {
         });
     }
 
-    private void writeLoginCredentials() {
-        GpodnetPreferences.setUsername(username);
-        GpodnetPreferences.setPassword(password);
-        GpodnetPreferences.setDeviceID(selectedDevice.getId());
-    }
-
     private void advance() {
         if (currentStep < STEP_FINISH) {
-
             View view = viewFlipper.getChildAt(currentStep + 1);
             if (currentStep == STEP_DEFAULT) {
                 setupHostView(view);
@@ -289,7 +288,10 @@ public class GpodderAuthenticationFragment extends DialogFragment {
                 if (selectedDevice == null) {
                     throw new IllegalStateException("Device must not be null here");
                 } else {
-                    writeLoginCredentials();
+                    SynchronizationSettings.setSelectedSyncProvider(SynchronizationProviderViewData.GPODDER_NET);
+                    SynchronizationCredentials.setUsername(username);
+                    SynchronizationCredentials.setPassword(password);
+                    SynchronizationCredentials.setDeviceID(selectedDevice.getId());
                     setupFinishView(view);
                 }
             }
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/NextcloudAuthenticationFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/NextcloudAuthenticationFragment.java
new file mode 100644
index 000000000..2e9260c1d
--- /dev/null
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/NextcloudAuthenticationFragment.java
@@ -0,0 +1,92 @@
+package de.danoeh.antennapod.fragment.preferences.synchronization;
+
+import android.app.Dialog;
+import android.content.DialogInterface;
+import android.os.Bundle;
+import android.view.View;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.appcompat.app.AlertDialog;
+import androidx.fragment.app.DialogFragment;
+import de.danoeh.antennapod.R;
+import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
+import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
+import de.danoeh.antennapod.core.sync.SynchronizationProviderViewData;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
+import de.danoeh.antennapod.databinding.NextcloudAuthDialogBinding;
+import de.danoeh.antennapod.net.sync.nextcloud.NextcloudLoginFlow;
+
+/**
+ * Guides the user through the authentication process.
+ */
+public class NextcloudAuthenticationFragment extends DialogFragment
+        implements NextcloudLoginFlow.AuthenticationCallback {
+    public static final String TAG = "NextcloudAuthenticationFragment";
+    private NextcloudAuthDialogBinding viewBinding;
+    private NextcloudLoginFlow nextcloudLoginFlow;
+    private boolean shouldDismiss = false;
+
+    @NonNull
+    @Override
+    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
+        AlertDialog.Builder dialog = new AlertDialog.Builder(getContext());
+        dialog.setTitle(R.string.gpodnetauth_login_butLabel);
+        dialog.setNegativeButton(R.string.cancel_label, null);
+        dialog.setCancelable(false);
+        this.setCancelable(false);
+
+        viewBinding = NextcloudAuthDialogBinding.inflate(getLayoutInflater());
+        dialog.setView(viewBinding.getRoot());
+
+        viewBinding.loginButton.setOnClickListener(v -> {
+            viewBinding.errorText.setVisibility(View.GONE);
+            viewBinding.loginButton.setVisibility(View.GONE);
+            viewBinding.loginProgressContainer.setVisibility(View.VISIBLE);
+            nextcloudLoginFlow = new NextcloudLoginFlow(AntennapodHttpClient.getHttpClient(),
+                    viewBinding.serverUrlText.getText().toString(), getContext(), this);
+            nextcloudLoginFlow.start();
+        });
+
+        return dialog.create();
+    }
+
+    @Override
+    public void onDismiss(@NonNull DialogInterface dialog) {
+        super.onDismiss(dialog);
+        if (nextcloudLoginFlow != null) {
+            nextcloudLoginFlow.cancel();
+        }
+    }
+
+    @Override
+    public void onResume() {
+        super.onResume();
+        if (shouldDismiss) {
+            dismiss();
+        }
+    }
+
+    @Override
+    public void onNextcloudAuthenticated(String server, String username, String password) {
+        SynchronizationSettings.setSelectedSyncProvider(SynchronizationProviderViewData.NEXTCLOUD_GPODDER);
+        SynchronizationCredentials.clear(getContext());
+        SynchronizationCredentials.setPassword(password);
+        SynchronizationCredentials.setHosturl(server);
+        SynchronizationCredentials.setUsername(username);
+        SyncService.fullSync(getContext());
+        if (isVisible()) {
+            dismiss();
+        } else {
+            shouldDismiss = true;
+        }
+    }
+
+    @Override
+    public void onNextcloudAuthError(String errorMessage) {
+        viewBinding.loginProgressContainer.setVisibility(View.GONE);
+        viewBinding.errorText.setVisibility(View.VISIBLE);
+        viewBinding.errorText.setText(errorMessage);
+        viewBinding.loginButton.setVisibility(View.VISIBLE);
+    }
+}
diff --git a/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/SynchronizationPreferencesFragment.java b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/SynchronizationPreferencesFragment.java
new file mode 100644
index 000000000..9b63b38ec
--- /dev/null
+++ b/app/src/main/java/de/danoeh/antennapod/fragment/preferences/synchronization/SynchronizationPreferencesFragment.java
@@ -0,0 +1,222 @@
+package de.danoeh.antennapod.fragment.preferences.synchronization;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.text.Spanned;
+import android.text.format.DateUtils;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.ArrayAdapter;
+import android.widget.ImageView;
+import android.widget.ListAdapter;
+import android.widget.TextView;
+
+import androidx.annotation.NonNull;
+import androidx.appcompat.app.AlertDialog;
+import androidx.core.text.HtmlCompat;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceFragmentCompat;
+
+import com.google.android.material.snackbar.Snackbar;
+
+import org.greenrobot.eventbus.EventBus;
+import org.greenrobot.eventbus.Subscribe;
+import org.greenrobot.eventbus.ThreadMode;
+
+import de.danoeh.antennapod.R;
+import de.danoeh.antennapod.activity.PreferenceActivity;
+import de.danoeh.antennapod.core.event.SyncServiceEvent;
+import de.danoeh.antennapod.core.sync.SynchronizationCredentials;
+import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.SynchronizationProviderViewData;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
+import de.danoeh.antennapod.dialog.AuthenticationDialog;
+
+public class SynchronizationPreferencesFragment extends PreferenceFragmentCompat {
+    private static final String PREFERENCE_SYNCHRONIZATION_DESCRIPTION = "preference_synchronization_description";
+    private static final String PREFERENCE_GPODNET_SETLOGIN_INFORMATION = "pref_gpodnet_setlogin_information";
+    private static final String PREFERENCE_SYNC = "pref_synchronization_sync";
+    private static final String PREFERENCE_FORCE_FULL_SYNC = "pref_synchronization_force_full_sync";
+    private static final String PREFERENCE_LOGOUT = "pref_synchronization_logout";
+
+    @Override
+    public void onCreatePreferences(Bundle savedInstanceState, String rootKey) {
+        addPreferencesFromResource(R.xml.preferences_synchronization);
+        setupScreen();
+        updateScreen();
+    }
+
+    @Override
+    public void onStart() {
+        super.onStart();
+        ((PreferenceActivity) getActivity()).getSupportActionBar().setTitle(R.string.synchronization_pref);
+        updateScreen();
+        EventBus.getDefault().register(this);
+    }
+
+    @Override
+    public void onStop() {
+        super.onStop();
+        EventBus.getDefault().unregister(this);
+        ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle("");
+    }
+
+    @Subscribe(threadMode = ThreadMode.MAIN, sticky = true)
+    public void syncStatusChanged(SyncServiceEvent event) {
+        if (!SynchronizationSettings.isProviderConnected()) {
+            return;
+        }
+        updateScreen();
+        if (event.getMessageResId() == R.string.sync_status_error
+                || event.getMessageResId() == R.string.sync_status_success) {
+            updateLastSyncReport(SynchronizationSettings.isLastSyncSuccessful(),
+                    SynchronizationSettings.getLastSyncAttempt());
+        } else {
+            ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle(event.getMessageResId());
+        }
+    }
+
+    private void setupScreen() {
+        final Activity activity = getActivity();
+        findPreference(PREFERENCE_GPODNET_SETLOGIN_INFORMATION)
+                .setOnPreferenceClickListener(preference -> {
+                    AuthenticationDialog dialog = new AuthenticationDialog(activity,
+                            R.string.pref_gpodnet_setlogin_information_title,
+                            false, SynchronizationCredentials.getUsername(), null) {
+                        @Override
+                        protected void onConfirmed(String username, String password) {
+                            SynchronizationCredentials.setPassword(password);
+                        }
+                    };
+                    dialog.show();
+                    return true;
+                });
+        findPreference(PREFERENCE_SYNC).setOnPreferenceClickListener(preference -> {
+            SyncService.syncImmediately(getActivity().getApplicationContext());
+            return true;
+        });
+        findPreference(PREFERENCE_FORCE_FULL_SYNC).setOnPreferenceClickListener(preference -> {
+            SyncService.fullSync(getContext());
+            return true;
+        });
+        findPreference(PREFERENCE_LOGOUT).setOnPreferenceClickListener(preference -> {
+            SynchronizationCredentials.clear(getContext());
+            Snackbar.make(getView(), R.string.pref_synchronization_logout_toast, Snackbar.LENGTH_LONG).show();
+            SynchronizationSettings.setSelectedSyncProvider(null);
+            updateScreen();
+            return true;
+        });
+    }
+
+    private void updateScreen() {
+        final boolean loggedIn = SynchronizationSettings.isProviderConnected();
+        Preference preferenceHeader = findPreference(PREFERENCE_SYNCHRONIZATION_DESCRIPTION);
+        if (loggedIn) {
+            SynchronizationProviderViewData selectedProvider =
+                    SynchronizationProviderViewData.fromIdentifier(getSelectedSyncProviderKey());
+            preferenceHeader.setTitle("");
+            preferenceHeader.setSummary(selectedProvider.getSummaryResource());
+            preferenceHeader.setIcon(selectedProvider.getIconResource());
+            preferenceHeader.setOnPreferenceClickListener(null);
+        } else {
+            preferenceHeader.setTitle(R.string.synchronization_choose_title);
+            preferenceHeader.setSummary(R.string.synchronization_summary_unchoosen);
+            preferenceHeader.setIcon(R.drawable.ic_cloud);
+            preferenceHeader.setOnPreferenceClickListener((preference) -> {
+                chooseProviderAndLogin();
+                return true;
+            });
+        }
+
+        Preference gpodnetSetLoginPreference = findPreference(PREFERENCE_GPODNET_SETLOGIN_INFORMATION);
+        gpodnetSetLoginPreference.setVisible(isProviderSelected(SynchronizationProviderViewData.GPODDER_NET));
+        gpodnetSetLoginPreference.setEnabled(loggedIn);
+        findPreference(PREFERENCE_SYNC).setEnabled(loggedIn);
+        findPreference(PREFERENCE_FORCE_FULL_SYNC).setEnabled(loggedIn);
+        findPreference(PREFERENCE_LOGOUT).setEnabled(loggedIn);
+        if (loggedIn) {
+            String summary = getString(R.string.synchronization_login_status,
+                    SynchronizationCredentials.getUsername(), SynchronizationCredentials.getHosturl());
+            Spanned formattedSummary = HtmlCompat.fromHtml(summary, HtmlCompat.FROM_HTML_MODE_LEGACY);
+            findPreference(PREFERENCE_LOGOUT).setSummary(formattedSummary);
+            updateLastSyncReport(SynchronizationSettings.isLastSyncSuccessful(),
+                    SynchronizationSettings.getLastSyncAttempt());
+        } else {
+            findPreference(PREFERENCE_LOGOUT).setSummary(null);
+            ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle(null);
+        }
+    }
+
+    private void chooseProviderAndLogin() {
+        AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
+        builder.setTitle(R.string.dialog_choose_sync_service_title);
+
+        SynchronizationProviderViewData[] providers = SynchronizationProviderViewData.values();
+        ListAdapter adapter = new ArrayAdapter<SynchronizationProviderViewData>(
+                getContext(), R.layout.alertdialog_sync_provider_chooser, providers) {
+
+            ViewHolder holder;
+
+            class ViewHolder {
+                ImageView icon;
+                TextView title;
+            }
+
+            public View getView(int position, View convertView, ViewGroup parent) {
+                final LayoutInflater inflater = LayoutInflater.from(getContext());
+                if (convertView == null) {
+                    convertView = inflater.inflate(
+                            R.layout.alertdialog_sync_provider_chooser, null);
+
+                    holder = new ViewHolder();
+                    holder.icon = (ImageView) convertView.findViewById(R.id.icon);
+                    holder.title = (TextView) convertView.findViewById(R.id.title);
+                    convertView.setTag(holder);
+                } else {
+                    holder = (ViewHolder) convertView.getTag();
+                }
+                SynchronizationProviderViewData synchronizationProviderViewData = getItem(position);
+                holder.title.setText(synchronizationProviderViewData.getSummaryResource());
+                holder.icon.setImageResource(synchronizationProviderViewData.getIconResource());
+                return convertView;
+            }
+        };
+
+        builder.setAdapter(adapter, (dialog, which) -> {
+            switch (providers[which]) {
+                case GPODDER_NET:
+                    new GpodderAuthenticationFragment()
+                            .show(getChildFragmentManager(), GpodderAuthenticationFragment.TAG);
+                    break;
+                case NEXTCLOUD_GPODDER:
+                    new NextcloudAuthenticationFragment()
+                            .show(getChildFragmentManager(), NextcloudAuthenticationFragment.TAG);
+                    break;
+                default:
+                    break;
+            }
+            updateScreen();
+        });
+
+        AlertDialog dialog = builder.create();
+        dialog.show();
+    }
+
+    private boolean isProviderSelected(@NonNull SynchronizationProviderViewData provider) {
+        String selectedSyncProviderKey = getSelectedSyncProviderKey();
+        return provider.getIdentifier().equals(selectedSyncProviderKey);
+    }
+
+    private String getSelectedSyncProviderKey() {
+        return SynchronizationSettings.getSelectedSyncProviderKey();
+    }
+
+    private void updateLastSyncReport(boolean successful, long lastTime) {
+        String status = String.format("%1$s (%2$s)", getString(successful
+                        ? R.string.gpodnetsync_pref_report_successful : R.string.gpodnetsync_pref_report_failed),
+                DateUtils.getRelativeDateTimeString(getContext(),
+                        lastTime, DateUtils.MINUTE_IN_MILLIS, DateUtils.WEEK_IN_MILLIS, DateUtils.FORMAT_SHOW_TIME));
+        ((PreferenceActivity) getActivity()).getSupportActionBar().setSubtitle(status);
+    }
+}
diff --git a/app/src/main/java/de/danoeh/antennapod/menuhandler/FeedItemMenuHandler.java b/app/src/main/java/de/danoeh/antennapod/menuhandler/FeedItemMenuHandler.java
index c272af7d5..23fdb86de 100644
--- a/app/src/main/java/de/danoeh/antennapod/menuhandler/FeedItemMenuHandler.java
+++ b/app/src/main/java/de/danoeh/antennapod/menuhandler/FeedItemMenuHandler.java
@@ -13,12 +13,12 @@ import com.google.android.material.snackbar.Snackbar;
 
 import de.danoeh.antennapod.R;
 import de.danoeh.antennapod.activity.MainActivity;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
 import de.danoeh.antennapod.core.preferences.PlaybackPreferences;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.core.service.playback.PlaybackService;
 import de.danoeh.antennapod.core.storage.DBWriter;
-import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
 import de.danoeh.antennapod.core.util.FeedItemUtil;
 import de.danoeh.antennapod.core.util.IntentUtils;
 import de.danoeh.antennapod.core.util.ShareUtils;
@@ -151,7 +151,7 @@ public class FeedItemMenuHandler {
         } else if (menuItemId == R.id.mark_read_item) {
             selectedItem.setPlayed(true);
             DBWriter.markItemPlayed(selectedItem, FeedItem.PLAYED, true);
-            if (GpodnetPreferences.loggedIn()) {
+            if (SynchronizationSettings.isProviderConnected()) {
                 FeedMedia media = selectedItem.getMedia();
                 // not all items have media, Gpodder only cares about those that do
                 if (media != null) {
@@ -161,17 +161,17 @@ public class FeedItemMenuHandler {
                             .position(media.getDuration() / 1000)
                             .total(media.getDuration() / 1000)
                             .build();
-                    SyncService.enqueueEpisodeAction(context, actionPlay);
+                    SynchronizationQueueSink.enqueueEpisodeActionIfSynchronizationIsActive(context, actionPlay);
                 }
             }
         } else if (menuItemId == R.id.mark_unread_item) {
             selectedItem.setPlayed(false);
             DBWriter.markItemPlayed(selectedItem, FeedItem.UNPLAYED, false);
-            if (GpodnetPreferences.loggedIn() && selectedItem.getMedia() != null) {
+            if (selectedItem.getMedia() != null) {
                 EpisodeAction actionNew = new EpisodeAction.Builder(selectedItem, EpisodeAction.NEW)
                         .currentTimestamp()
                         .build();
-                SyncService.enqueueEpisodeAction(context, actionNew);
+                SynchronizationQueueSink.enqueueEpisodeActionIfSynchronizationIsActive(context, actionNew);
             }
         } else if (menuItemId == R.id.add_to_queue_item) {
             DBWriter.addQueueItem(context, selectedItem);
diff --git a/app/src/main/res/layout/alertdialog_sync_provider_chooser.xml b/app/src/main/res/layout/alertdialog_sync_provider_chooser.xml
new file mode 100644
index 000000000..9b4d62804
--- /dev/null
+++ b/app/src/main/res/layout/alertdialog_sync_provider_chooser.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="fill_parent"
+    android:layout_height="wrap_content"
+    android:orientation="horizontal"
+    android:padding="16dp">
+
+    <ImageView
+        android:id="@+id/icon"
+        android:layout_width="48dp"
+        android:layout_height="48dp"
+        android:layout_marginRight="16dip"
+        android:layout_marginEnd="16dip"
+        android:layout_gravity="center_vertical" />
+
+    <TextView
+        android:id="@+id/title"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text=""
+        android:layout_gravity="center" />
+
+</LinearLayout>
diff --git a/app/src/main/res/layout/nextcloud_auth_dialog.xml b/app/src/main/res/layout/nextcloud_auth_dialog.xml
new file mode 100644
index 000000000..345eec88b
--- /dev/null
+++ b/app/src/main/res/layout/nextcloud_auth_dialog.xml
@@ -0,0 +1,63 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:padding="16dp"
+    android:orientation="vertical"
+    android:clipToPadding="false">
+
+    <com.google.android.material.textfield.TextInputLayout
+        android:id="@+id/serverUrlTextInput"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="16dp"
+        style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox">
+
+        <com.google.android.material.textfield.TextInputEditText
+            android:id="@+id/serverUrlText"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:hint="@string/gpodnetauth_host"
+            android:inputType="textNoSuggestions"
+            android:lines="1"
+            android:imeOptions="actionNext|flagNoFullscreen" />
+
+    </com.google.android.material.textfield.TextInputLayout>
+
+    <LinearLayout
+        android:id="@+id/loginProgressContainer"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:visibility="gone"
+        android:orientation="horizontal"
+        android:layout_gravity="center_vertical">
+
+        <ProgressBar
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginEnd="8dp"
+            android:layout_marginRight="8dp" />
+
+        <TextView
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="@string/synchronization_nextcloud_authenticate_browser" />
+
+    </LinearLayout>
+
+    <TextView
+        android:id="@+id/errorText"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:visibility="gone"
+        android:textColor="@color/download_failed_red"
+        android:layout_marginBottom="16dp" />
+
+    <Button
+        android:id="@+id/loginButton"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/gpodnetauth_login_butLabel" />
+
+</LinearLayout>
diff --git a/app/src/main/res/xml/preferences.xml b/app/src/main/res/xml/preferences.xml
index d528945c7..7c5012899 100644
--- a/app/src/main/res/xml/preferences.xml
+++ b/app/src/main/res/xml/preferences.xml
@@ -28,7 +28,7 @@
             android:icon="@drawable/ic_network" />
 
     <Preference
-            android:key="prefScreenGpodder"
+            android:key="prefScreenSynchronization"
             android:title="@string/synchronization_pref"
             android:summary="@string/synchronization_sum"
             android:icon="@drawable/ic_cloud" />
diff --git a/app/src/main/res/xml/preferences_gpodder.xml b/app/src/main/res/xml/preferences_gpodder.xml
deleted file mode 100644
index a210b8e11..000000000
--- a/app/src/main/res/xml/preferences_gpodder.xml
+++ /dev/null
@@ -1,28 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<PreferenceScreen
-        xmlns:android="http://schemas.android.com/apk/res/android">
-    <Preference
-            android:key="pref_gpodnet_description"
-            android:icon="@drawable/gpodder_icon"
-            android:summary="@string/gpodnet_description"/>
-    <Preference
-            android:key="pref_gpodnet_authenticate"
-            android:title="@string/pref_gpodnet_authenticate_title"
-            android:summary="@string/pref_gpodnet_authenticate_sum"/>
-    <Preference
-            android:key="pref_gpodnet_setlogin_information"
-            android:title="@string/pref_gpodnet_setlogin_information_title"
-            android:summary="@string/pref_gpodnet_setlogin_information_sum"/>
-    <Preference
-            android:key="pref_gpodnet_sync"
-            android:title="@string/pref_gpodnet_sync_changes_title"
-            android:summary="@string/pref_gpodnet_sync_changes_sum"/>
-    <Preference
-            android:key="pref_gpodnet_force_full_sync"
-            android:title="@string/pref_gpodnet_full_sync_title"
-            android:summary="@string/pref_gpodnet_full_sync_sum"/>
-    <Preference
-            android:key="pref_gpodnet_logout"
-            android:title="@string/pref_gpodnet_logout_title"/>
-
-</PreferenceScreen>
diff --git a/app/src/main/res/xml/preferences_synchronization.xml b/app/src/main/res/xml/preferences_synchronization.xml
new file mode 100644
index 000000000..fbd4ccc79
--- /dev/null
+++ b/app/src/main/res/xml/preferences_synchronization.xml
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<PreferenceScreen
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
+
+    <Preference
+        android:key="preference_synchronization_description"
+        android:icon="@drawable/ic_notification_sync"
+        android:summary="@string/synchronization_summary_unchoosen"/>
+
+    <Preference
+        android:key="pref_gpodnet_setlogin_information"
+        android:title="@string/pref_gpodnet_setlogin_information_title"
+        android:summary="@string/pref_gpodnet_setlogin_information_sum"
+        app:isPreferenceVisible="false"/>
+
+    <Preference
+        android:key="pref_synchronization_sync"
+        android:title="@string/synchronization_sync_changes_title"
+        android:summary="@string/synchronization_sync_summary"/>
+
+    <Preference
+        android:key="pref_synchronization_force_full_sync"
+        android:title="@string/synchronization_full_sync_title"
+        android:summary="@string/synchronization_force_sync_summary"/>
+
+    <Preference
+        android:key="pref_synchronization_logout"
+        android:title="@string/synchronization_logout"/>
+
+</PreferenceScreen>
diff --git a/core/src/main/java/de/danoeh/antennapod/core/preferences/GpodnetPreferences.java b/core/src/main/java/de/danoeh/antennapod/core/preferences/GpodnetPreferences.java
deleted file mode 100644
index e338e0d01..000000000
--- a/core/src/main/java/de/danoeh/antennapod/core/preferences/GpodnetPreferences.java
+++ /dev/null
@@ -1,115 +0,0 @@
-package de.danoeh.antennapod.core.preferences;
-
-import android.content.Context;
-import android.content.SharedPreferences;
-import android.util.Log;
-import de.danoeh.antennapod.core.BuildConfig;
-import de.danoeh.antennapod.core.ClientConfig;
-import de.danoeh.antennapod.core.sync.SyncService;
-import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
-
-/**
- * Manages preferences for accessing gpodder.net service
- */
-public class GpodnetPreferences {
-
-    private GpodnetPreferences(){}
-
-    private static final String TAG = "GpodnetPreferences";
-
-    private static final String PREF_NAME = "gpodder.net";
-    private static final String PREF_GPODNET_USERNAME = "de.danoeh.antennapod.preferences.gpoddernet.username";
-    private static final String PREF_GPODNET_PASSWORD = "de.danoeh.antennapod.preferences.gpoddernet.password";
-    private static final String PREF_GPODNET_DEVICEID = "de.danoeh.antennapod.preferences.gpoddernet.deviceID";
-    private static final String PREF_GPODNET_HOSTNAME = "prefGpodnetHostname";
-
-    private static String username;
-    private static String password;
-    private static String deviceID;
-    private static String hosturl;
-
-    private static boolean preferencesLoaded = false;
-
-    private static SharedPreferences getPreferences() {
-        return ClientConfig.applicationCallbacks.getApplicationInstance().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-    }
-
-    private static synchronized void ensurePreferencesLoaded() {
-        if (!preferencesLoaded) {
-            SharedPreferences prefs = getPreferences();
-            username = prefs.getString(PREF_GPODNET_USERNAME, null);
-            password = prefs.getString(PREF_GPODNET_PASSWORD, null);
-            deviceID = prefs.getString(PREF_GPODNET_DEVICEID, null);
-            hosturl = prefs.getString(PREF_GPODNET_HOSTNAME, GpodnetService.DEFAULT_BASE_HOST);
-
-            preferencesLoaded = true;
-        }
-    }
-
-    private static void writePreference(String key, String value) {
-        SharedPreferences.Editor editor = getPreferences().edit();
-        editor.putString(key, value);
-        editor.apply();
-    }
-
-    public static String getUsername() {
-        ensurePreferencesLoaded();
-        return username;
-    }
-
-    public static void setUsername(String username) {
-        GpodnetPreferences.username = username;
-        writePreference(PREF_GPODNET_USERNAME, username);
-    }
-
-    public static String getPassword() {
-        ensurePreferencesLoaded();
-        return password;
-    }
-
-    public static void setPassword(String password) {
-        GpodnetPreferences.password = password;
-        writePreference(PREF_GPODNET_PASSWORD, password);
-    }
-
-    public static String getDeviceID() {
-        ensurePreferencesLoaded();
-        return deviceID;
-    }
-
-    public static void setDeviceID(String deviceID) {
-        GpodnetPreferences.deviceID = deviceID;
-        writePreference(PREF_GPODNET_DEVICEID, deviceID);
-    }
-
-    public static String getHosturl() {
-        ensurePreferencesLoaded();
-        return hosturl;
-    }
-
-    public static void setHosturl(String value) {
-        if (!value.equals(hosturl)) {
-            logout();
-            writePreference(PREF_GPODNET_HOSTNAME, value);
-            hosturl = value;
-        }
-    }
-
-    /**
-     * Returns true if device ID, username and password have a non-null value
-     */
-    public static boolean loggedIn() {
-        ensurePreferencesLoaded();
-        return deviceID != null && username != null && password != null;
-    }
-
-    public static synchronized void logout() {
-        if (BuildConfig.DEBUG) Log.d(TAG, "Logout: Clearing preferences");
-        setUsername(null);
-        setPassword(null);
-        setDeviceID(null);
-        SyncService.clearQueue(ClientConfig.applicationCallbacks.getApplicationInstance());
-        UserPreferences.setGpodnetNotificationsEnabled();
-    }
-
-}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/MediaDownloadedHandler.java b/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/MediaDownloadedHandler.java
index 8c9035621..6bbd704e2 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/MediaDownloadedHandler.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/service/download/handler/MediaDownloadedHandler.java
@@ -6,21 +6,22 @@ import android.util.Log;
 
 import androidx.annotation.NonNull;
 
+import org.greenrobot.eventbus.EventBus;
+
 import java.io.File;
 import java.util.concurrent.ExecutionException;
 
 import de.danoeh.antennapod.core.event.UnreadItemsUpdateEvent;
-import de.danoeh.antennapod.model.feed.FeedItem;
-import de.danoeh.antennapod.model.feed.FeedMedia;
 import de.danoeh.antennapod.core.service.download.DownloadRequest;
 import de.danoeh.antennapod.core.service.download.DownloadStatus;
 import de.danoeh.antennapod.core.storage.DBReader;
 import de.danoeh.antennapod.core.storage.DBWriter;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
 import de.danoeh.antennapod.core.util.ChapterUtils;
 import de.danoeh.antennapod.core.util.DownloadError;
-import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.model.feed.FeedItem;
+import de.danoeh.antennapod.model.feed.FeedMedia;
 import de.danoeh.antennapod.net.sync.model.EpisodeAction;
-import org.greenrobot.eventbus.EventBus;
 
 /**
  * Handles a completed media download.
@@ -103,7 +104,7 @@ public class MediaDownloadedHandler implements Runnable {
             EpisodeAction action = new EpisodeAction.Builder(item, EpisodeAction.DOWNLOAD)
                     .currentTimestamp()
                     .build();
-            SyncService.enqueueEpisodeAction(context, action);
+            SynchronizationQueueSink.enqueueEpisodeActionIfSynchronizationIsActive(context, action);
         }
     }
 
diff --git a/core/src/main/java/de/danoeh/antennapod/core/service/playback/PlaybackService.java b/core/src/main/java/de/danoeh/antennapod/core/service/playback/PlaybackService.java
index f503c16f4..848ea7cfc 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/service/playback/PlaybackService.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/service/playback/PlaybackService.java
@@ -1,5 +1,7 @@
 package de.danoeh.antennapod.core.service.playback;
 
+import static de.danoeh.antennapod.model.feed.FeedPreferences.SPEED_USE_GLOBAL;
+
 import android.app.NotificationManager;
 import android.app.PendingIntent;
 import android.app.Service;
@@ -21,13 +23,7 @@ import android.os.Build;
 import android.os.Bundle;
 import android.os.IBinder;
 import android.os.Vibrator;
-import androidx.preference.PreferenceManager;
-import androidx.annotation.NonNull;
-import androidx.annotation.StringRes;
-import androidx.core.app.NotificationCompat;
-import androidx.core.app.NotificationManagerCompat;
 import android.support.v4.media.MediaBrowserCompat;
-import androidx.media.MediaBrowserServiceCompat;
 import android.support.v4.media.MediaDescriptionCompat;
 import android.support.v4.media.MediaMetadataCompat;
 import android.support.v4.media.session.MediaSessionCompat;
@@ -40,6 +36,17 @@ import android.view.SurfaceHolder;
 import android.webkit.URLUtil;
 import android.widget.Toast;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.StringRes;
+import androidx.core.app.NotificationCompat;
+import androidx.core.app.NotificationManagerCompat;
+import androidx.media.MediaBrowserServiceCompat;
+import androidx.preference.PreferenceManager;
+
+import org.greenrobot.eventbus.EventBus;
+import org.greenrobot.eventbus.Subscribe;
+import org.greenrobot.eventbus.ThreadMode;
+
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -52,12 +59,6 @@ import de.danoeh.antennapod.core.event.ServiceEvent;
 import de.danoeh.antennapod.core.event.settings.SkipIntroEndingChangedEvent;
 import de.danoeh.antennapod.core.event.settings.SpeedPresetChangedEvent;
 import de.danoeh.antennapod.core.event.settings.VolumeAdaptionChangedEvent;
-import de.danoeh.antennapod.model.feed.Chapter;
-import de.danoeh.antennapod.model.feed.Feed;
-import de.danoeh.antennapod.model.feed.FeedItem;
-import de.danoeh.antennapod.model.feed.FeedMedia;
-import de.danoeh.antennapod.model.feed.FeedPreferences;
-import de.danoeh.antennapod.model.playback.MediaType;
 import de.danoeh.antennapod.core.preferences.PlaybackPreferences;
 import de.danoeh.antennapod.core.preferences.SleepTimerPreferences;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
@@ -66,15 +67,21 @@ import de.danoeh.antennapod.core.storage.DBReader;
 import de.danoeh.antennapod.core.storage.DBTasks;
 import de.danoeh.antennapod.core.storage.DBWriter;
 import de.danoeh.antennapod.core.storage.FeedSearcher;
-import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
 import de.danoeh.antennapod.core.util.FeedItemUtil;
 import de.danoeh.antennapod.core.util.IntentUtils;
 import de.danoeh.antennapod.core.util.NetworkUtils;
 import de.danoeh.antennapod.core.util.gui.NotificationUtils;
-import de.danoeh.antennapod.model.playback.Playable;
 import de.danoeh.antennapod.core.util.playback.PlayableUtils;
 import de.danoeh.antennapod.core.util.playback.PlaybackServiceStarter;
 import de.danoeh.antennapod.core.widget.WidgetUpdater;
+import de.danoeh.antennapod.model.feed.Chapter;
+import de.danoeh.antennapod.model.feed.Feed;
+import de.danoeh.antennapod.model.feed.FeedItem;
+import de.danoeh.antennapod.model.feed.FeedMedia;
+import de.danoeh.antennapod.model.feed.FeedPreferences;
+import de.danoeh.antennapod.model.playback.MediaType;
+import de.danoeh.antennapod.model.playback.Playable;
 import de.danoeh.antennapod.ui.appstartintent.MainActivityStarter;
 import de.danoeh.antennapod.ui.appstartintent.VideoPlayerActivityStarter;
 import io.reactivex.Completable;
@@ -83,11 +90,6 @@ import io.reactivex.Single;
 import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.schedulers.Schedulers;
-import org.greenrobot.eventbus.EventBus;
-import org.greenrobot.eventbus.Subscribe;
-import org.greenrobot.eventbus.ThreadMode;
-
-import static de.danoeh.antennapod.model.feed.FeedPreferences.SPEED_USE_GLOBAL;
 
 /**
  * Controls the MediaPlayer that plays a FeedMedia-file
@@ -966,7 +968,8 @@ public class PlaybackService extends MediaBrowserServiceCompat {
             taskManager.cancelWidgetUpdater();
             if (playable != null) {
                 if (playable instanceof FeedMedia) {
-                    SyncService.enqueueEpisodePlayed(getApplicationContext(), (FeedMedia) playable, false);
+                    SynchronizationQueueSink.enqueueEpisodePlayedIfSynchronizationIsActive(getApplicationContext(),
+                            (FeedMedia) playable, false);
                 }
                 playable.onPlaybackPause(getApplicationContext());
             }
@@ -1110,10 +1113,12 @@ public class PlaybackService extends MediaBrowserServiceCompat {
         }
 
         if (ended || smartMarkAsPlayed) {
-            SyncService.enqueueEpisodePlayed(getApplicationContext(), media, true);
+            SynchronizationQueueSink.enqueueEpisodePlayedIfSynchronizationIsActive(
+                    getApplicationContext(), media, true);
             media.onPlaybackCompleted(getApplicationContext());
         } else {
-            SyncService.enqueueEpisodePlayed(getApplicationContext(), media, false);
+            SynchronizationQueueSink.enqueueEpisodePlayedIfSynchronizationIsActive(
+                    getApplicationContext(), media, false);
             media.onPlaybackPause(getApplicationContext());
         }
 
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java b/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
index 185d85e7a..f776fe111 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
@@ -575,7 +575,6 @@ public final class DBReader {
     @Nullable
     private static FeedItem getFeedItemByGuidOrEpisodeUrl(final String guid, final String episodeUrl,
             PodDBAdapter adapter) {
-        Log.d(TAG, "Loading feeditem with guid " + guid + " or episode url " + episodeUrl);
         try (Cursor cursor = adapter.getFeedItemCursor(guid, episodeUrl)) {
             if (!cursor.moveToNext()) {
                 return null;
@@ -633,8 +632,6 @@ public final class DBReader {
      *          Does NOT load additional attributes like feed or queue state.
      */
     public static FeedItem getFeedItemByGuidOrEpisodeUrl(final String guid, final String episodeUrl) {
-        Log.d(TAG, "getFeedItem() called with: " + "guid = [" + guid + "], episodeUrl = [" + episodeUrl + "]");
-
         PodDBAdapter adapter = PodDBAdapter.getInstance();
         adapter.open();
         try {
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/DBTasks.java b/core/src/main/java/de/danoeh/antennapod/core/storage/DBTasks.java
index 9dd979dc7..377202c4b 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/DBTasks.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/DBTasks.java
@@ -1,5 +1,7 @@
 package de.danoeh.antennapod.core.storage;
 
+import static android.content.Context.MODE_PRIVATE;
+
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.database.Cursor;
@@ -9,22 +11,6 @@ import android.util.Log;
 
 import androidx.annotation.VisibleForTesting;
 
-import de.danoeh.antennapod.core.R;
-import de.danoeh.antennapod.core.event.FeedItemEvent;
-import de.danoeh.antennapod.core.event.FeedListUpdateEvent;
-import de.danoeh.antennapod.core.event.MessageEvent;
-import de.danoeh.antennapod.model.feed.Feed;
-import de.danoeh.antennapod.model.feed.FeedItem;
-import de.danoeh.antennapod.model.feed.FeedMedia;
-import de.danoeh.antennapod.core.feed.LocalFeedUpdater;
-import de.danoeh.antennapod.core.preferences.UserPreferences;
-import de.danoeh.antennapod.core.service.download.DownloadStatus;
-import de.danoeh.antennapod.core.storage.mapper.FeedCursorMapper;
-import de.danoeh.antennapod.core.sync.SyncService;
-import de.danoeh.antennapod.core.util.DownloadError;
-import de.danoeh.antennapod.core.util.LongList;
-import de.danoeh.antennapod.core.util.comparator.FeedItemPubdateComparator;
-import de.danoeh.antennapod.net.sync.model.EpisodeAction;
 import org.greenrobot.eventbus.EventBus;
 
 import java.util.ArrayList;
@@ -41,7 +27,23 @@ import java.util.concurrent.Future;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.atomic.AtomicBoolean;
 
-import static android.content.Context.MODE_PRIVATE;
+import de.danoeh.antennapod.core.R;
+import de.danoeh.antennapod.core.event.FeedItemEvent;
+import de.danoeh.antennapod.core.event.FeedListUpdateEvent;
+import de.danoeh.antennapod.core.event.MessageEvent;
+import de.danoeh.antennapod.core.feed.LocalFeedUpdater;
+import de.danoeh.antennapod.core.preferences.UserPreferences;
+import de.danoeh.antennapod.core.service.download.DownloadStatus;
+import de.danoeh.antennapod.core.storage.mapper.FeedCursorMapper;
+import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
+import de.danoeh.antennapod.core.util.DownloadError;
+import de.danoeh.antennapod.core.util.LongList;
+import de.danoeh.antennapod.core.util.comparator.FeedItemPubdateComparator;
+import de.danoeh.antennapod.model.feed.Feed;
+import de.danoeh.antennapod.model.feed.FeedItem;
+import de.danoeh.antennapod.model.feed.FeedMedia;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
 
 /**
  * Provides methods for doing common tasks that use DBReader and DBWriter.
@@ -482,7 +484,7 @@ public final class DBTasks {
                                     .position(oldItem.getMedia().getDuration() / 1000)
                                     .total(oldItem.getMedia().getDuration() / 1000)
                                     .build();
-                            SyncService.enqueueEpisodeAction(context, action);
+                            SynchronizationQueueSink.enqueueEpisodeActionIfSynchronizationIsActive(context, action);
                         }
                     }
                 }
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java b/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
index 34ea5e207..479a7763c 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
@@ -7,8 +7,6 @@ import android.util.Log;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
-import de.danoeh.antennapod.core.sync.SyncService;
-import de.danoeh.antennapod.net.sync.model.EpisodeAction;
 import org.greenrobot.eventbus.EventBus;
 
 import java.io.File;
@@ -32,23 +30,24 @@ import de.danoeh.antennapod.core.event.MessageEvent;
 import de.danoeh.antennapod.core.event.PlaybackHistoryEvent;
 import de.danoeh.antennapod.core.event.QueueEvent;
 import de.danoeh.antennapod.core.event.UnreadItemsUpdateEvent;
-import de.danoeh.antennapod.model.feed.Feed;
 import de.danoeh.antennapod.core.feed.FeedEvent;
-import de.danoeh.antennapod.model.feed.FeedItem;
-import de.danoeh.antennapod.model.feed.FeedMedia;
-import de.danoeh.antennapod.model.feed.FeedPreferences;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
 import de.danoeh.antennapod.core.preferences.PlaybackPreferences;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.core.service.download.DownloadStatus;
 import de.danoeh.antennapod.core.service.playback.PlaybackService;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
 import de.danoeh.antennapod.core.util.FeedItemPermutors;
 import de.danoeh.antennapod.core.util.IntentUtils;
 import de.danoeh.antennapod.core.util.LongList;
 import de.danoeh.antennapod.core.util.Permutor;
+import de.danoeh.antennapod.core.util.playback.PlayableUtils;
+import de.danoeh.antennapod.model.feed.Feed;
+import de.danoeh.antennapod.model.feed.FeedItem;
+import de.danoeh.antennapod.model.feed.FeedMedia;
+import de.danoeh.antennapod.model.feed.FeedPreferences;
 import de.danoeh.antennapod.model.feed.SortOrder;
 import de.danoeh.antennapod.model.playback.Playable;
-import de.danoeh.antennapod.core.util.playback.PlayableUtils;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
 
 /**
  * Provides methods for writing data to AntennaPod's database.
@@ -132,13 +131,11 @@ public class DBWriter {
             }
 
             // Gpodder: queue delete action for synchronization
-            if (GpodnetPreferences.loggedIn()) {
-                FeedItem item = media.getItem();
-                EpisodeAction action = new EpisodeAction.Builder(item, EpisodeAction.DELETE)
-                        .currentTimestamp()
-                        .build();
-                SyncService.enqueueEpisodeAction(context, action);
-            }
+            FeedItem item = media.getItem();
+            EpisodeAction action = new EpisodeAction.Builder(item, EpisodeAction.DELETE)
+                    .currentTimestamp()
+                    .build();
+            SynchronizationQueueSink.enqueueEpisodeActionIfSynchronizationIsActive(context, action);
         }
         EventBus.getDefault().post(FeedItemEvent.deletedMedia(Collections.singletonList(media.getItem())));
         return true;
@@ -170,7 +167,7 @@ public class DBWriter {
             adapter.removeFeed(feed);
             adapter.close();
 
-            SyncService.enqueueFeedRemoved(context, feed.getDownload_url());
+            SynchronizationQueueSink.enqueueFeedRemovedIfSynchronizationIsActive(context, feed.getDownload_url());
             EventBus.getDefault().post(new FeedListUpdateEvent(feed));
         });
     }
@@ -782,7 +779,7 @@ public class DBWriter {
             adapter.close();
 
             for (Feed feed : feeds) {
-                SyncService.enqueueFeedAdded(context, feed.getDownload_url());
+                SynchronizationQueueSink.enqueueFeedAddedIfSynchronizationIsActive(context, feed.getDownload_url());
             }
 
             BackupManager backupManager = new BackupManager(context);
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java b/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
index 85ce2dc99..55cfafbbb 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
@@ -1123,7 +1123,6 @@ public class PodDBAdapter {
                 + " INNER JOIN " + TABLE_NAME_FEEDS
                 + " ON " + TABLE_NAME_FEED_ITEMS + "." + KEY_FEED + "=" + TABLE_NAME_FEEDS + "." + KEY_ID
                 + " WHERE " + whereClauseCondition;
-        Log.d(TAG, "SQL: " + query);
         return db.rawQuery(query, null);
     }
 
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java b/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java
index 6d80a6457..74e5d5cdf 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java
@@ -4,7 +4,8 @@ public class GuidValidator {
 
     public static boolean isValidGuid(String guid) {
         return guid != null
-                && !guid.trim().isEmpty();
+                && !guid.trim().isEmpty()
+                && !guid.equals("null");
     }
 }
 
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/LockingAsyncExecutor.java b/core/src/main/java/de/danoeh/antennapod/core/sync/LockingAsyncExecutor.java
new file mode 100644
index 000000000..e7dbbbd3c
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/LockingAsyncExecutor.java
@@ -0,0 +1,35 @@
+package de.danoeh.antennapod.core.sync;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+import io.reactivex.Completable;
+import io.reactivex.schedulers.Schedulers;
+
+public class LockingAsyncExecutor {
+
+    static final ReentrantLock lock = new ReentrantLock();
+
+    /**
+     * Take the lock and execute runnable (to prevent changes to preferences being lost when enqueueing while sync is
+     * in progress). If the lock is free, the runnable is directly executed in the calling thread to prevent overhead.
+     */
+    public static void executeLockedAsync(Runnable runnable) {
+        if (lock.tryLock()) {
+            try {
+                runnable.run();
+            } finally {
+                lock.unlock();
+            }
+        } else {
+            Completable.fromRunnable(() -> {
+                lock.lock();
+                try {
+                    runnable.run();
+                } finally {
+                    lock.unlock();
+                }
+            }).subscribeOn(Schedulers.io())
+                    .subscribe();
+        }
+    }
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java b/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
index 9803a29db..8edc37ac4 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
@@ -5,7 +5,6 @@ import android.app.NotificationManager;
 import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
-import android.content.SharedPreferences;
 import android.util.Log;
 
 import androidx.annotation.NonNull;
@@ -20,12 +19,16 @@ import androidx.work.WorkManager;
 import androidx.work.Worker;
 import androidx.work.WorkerParameters;
 
+import org.apache.commons.lang3.StringUtils;
+import org.greenrobot.eventbus.EventBus;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
 import de.danoeh.antennapod.core.R;
 import de.danoeh.antennapod.core.event.SyncServiceEvent;
-import de.danoeh.antennapod.model.feed.Feed;
-import de.danoeh.antennapod.model.feed.FeedItem;
-import de.danoeh.antennapod.model.feed.FeedMedia;
-import de.danoeh.antennapod.core.preferences.GpodnetPreferences;
 import de.danoeh.antennapod.core.preferences.UserPreferences;
 import de.danoeh.antennapod.core.service.download.AntennapodHttpClient;
 import de.danoeh.antennapod.core.storage.DBReader;
@@ -33,10 +36,14 @@ import de.danoeh.antennapod.core.storage.DBTasks;
 import de.danoeh.antennapod.core.storage.DBWriter;
 import de.danoeh.antennapod.core.storage.DownloadRequestException;
 import de.danoeh.antennapod.core.storage.DownloadRequester;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueStorage;
 import de.danoeh.antennapod.core.util.FeedItemUtil;
 import de.danoeh.antennapod.core.util.LongList;
 import de.danoeh.antennapod.core.util.URLChecker;
 import de.danoeh.antennapod.core.util.gui.NotificationUtils;
+import de.danoeh.antennapod.model.feed.Feed;
+import de.danoeh.antennapod.model.feed.FeedItem;
+import de.danoeh.antennapod.model.feed.FeedMedia;
 import de.danoeh.antennapod.net.sync.gpoddernet.GpodnetService;
 import de.danoeh.antennapod.net.sync.model.EpisodeAction;
 import de.danoeh.antennapod.net.sync.model.EpisodeActionChanges;
@@ -44,156 +51,54 @@ import de.danoeh.antennapod.net.sync.model.ISyncService;
 import de.danoeh.antennapod.net.sync.model.SubscriptionChanges;
 import de.danoeh.antennapod.net.sync.model.SyncServiceException;
 import de.danoeh.antennapod.net.sync.model.UploadChangesResponse;
-import io.reactivex.Completable;
-import io.reactivex.schedulers.Schedulers;
-
-import org.apache.commons.lang3.StringUtils;
-import org.greenrobot.eventbus.EventBus;
-import org.json.JSONArray;
-import org.json.JSONException;
-
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.locks.ReentrantLock;
+import de.danoeh.antennapod.net.sync.nextcloud.NextcloudSyncService;
 
 public class SyncService extends Worker {
-    private static final String PREF_NAME = "SyncService";
-    private static final String PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP = "last_sync_timestamp";
-    private static final String PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP = "last_episode_actions_sync_timestamp";
-    private static final String PREF_QUEUED_FEEDS_ADDED = "sync_added";
-    private static final String PREF_QUEUED_FEEDS_REMOVED = "sync_removed";
-    private static final String PREF_QUEUED_EPISODE_ACTIONS = "sync_queued_episode_actions";
-    private static final String PREF_LAST_SYNC_ATTEMPT_TIMESTAMP = "last_sync_attempt_timestamp";
-    private static final String PREF_LAST_SYNC_ATTEMPT_SUCCESS = "last_sync_attempt_success";
-    private static final String TAG = "SyncService";
-    private static final String WORK_ID_SYNC = "SyncServiceWorkId";
-    private static final ReentrantLock lock = new ReentrantLock();
+    public static final String TAG = "SyncService";
 
-    private ISyncService syncServiceImpl;
+    private static final String WORK_ID_SYNC = "SyncServiceWorkId";
+    private final SynchronizationQueueStorage synchronizationQueueStorage;
 
     public SyncService(@NonNull Context context, @NonNull WorkerParameters params) {
         super(context, params);
+        synchronizationQueueStorage = new SynchronizationQueueStorage(context);
     }
 
     @Override
     @NonNull
     public Result doWork() {
-        if (!GpodnetPreferences.loggedIn()) {
+        ISyncService activeSyncProvider = getActiveSyncProvider();
+        if (activeSyncProvider == null) {
             return Result.success();
         }
-        syncServiceImpl = new GpodnetService(AntennapodHttpClient.getHttpClient(),
-                GpodnetPreferences.getHosturl(), GpodnetPreferences.getDeviceID(),
-                GpodnetPreferences.getUsername(), GpodnetPreferences.getPassword());
-        SharedPreferences.Editor prefs = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE)
-                .edit();
-        prefs.putLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, System.currentTimeMillis()).apply();
+
+        SynchronizationSettings.updateLastSynchronizationAttempt();
         try {
-            syncServiceImpl.login();
+            activeSyncProvider.login();
             EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_subscriptions));
-            syncSubscriptions();
-            syncEpisodeActions();
-            syncServiceImpl.logout();
+            syncSubscriptions(activeSyncProvider);
+            syncEpisodeActions(activeSyncProvider);
+            activeSyncProvider.logout();
             clearErrorNotifications();
             EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_success));
-            prefs.putBoolean(PREF_LAST_SYNC_ATTEMPT_SUCCESS, true).apply();
+            SynchronizationSettings.setLastSynchronizationAttemptSuccess(true);
             return Result.success();
-        } catch (SyncServiceException e) {
+        } catch (Exception e) {
             EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_error));
-            prefs.putBoolean(PREF_LAST_SYNC_ATTEMPT_SUCCESS, false).apply();
+            SynchronizationSettings.setLastSynchronizationAttemptSuccess(false);
             Log.e(TAG, Log.getStackTraceString(e));
-            if (getRunAttemptCount() % 3 == 2) {
-                // Do not spam users with notification and retry before notifying
-                updateErrorNotification(e);
-            }
-            return Result.retry();
-        }
-    }
-
-    public static void clearQueue(Context context) {
-        executeLockedAsync(() ->
-                context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                        .putLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0)
-                        .putLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0)
-                        .putLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, 0)
-                        .putString(PREF_QUEUED_EPISODE_ACTIONS, "[]")
-                        .putString(PREF_QUEUED_FEEDS_ADDED, "[]")
-                        .putString(PREF_QUEUED_FEEDS_REMOVED, "[]")
-                        .apply());
-    }
 
-    public static void enqueueFeedAdded(Context context, String downloadUrl) {
-        if (!GpodnetPreferences.loggedIn()) {
-            return;
-        }
-        executeLockedAsync(() -> {
-            try {
-                SharedPreferences prefs = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-                String json = prefs.getString(PREF_QUEUED_FEEDS_ADDED, "[]");
-                JSONArray queue = new JSONArray(json);
-                queue.put(downloadUrl);
-                prefs.edit().putString(PREF_QUEUED_FEEDS_ADDED, queue.toString()).apply();
-            } catch (JSONException e) {
-                e.printStackTrace();
-            }
-            sync(context);
-        });
-    }
-
-    public static void enqueueFeedRemoved(Context context, String downloadUrl) {
-        if (!GpodnetPreferences.loggedIn()) {
-            return;
-        }
-        executeLockedAsync(() -> {
-            try {
-                SharedPreferences prefs = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-                String json = prefs.getString(PREF_QUEUED_FEEDS_REMOVED, "[]");
-                JSONArray queue = new JSONArray(json);
-                queue.put(downloadUrl);
-                prefs.edit().putString(PREF_QUEUED_FEEDS_REMOVED, queue.toString()).apply();
-            } catch (JSONException e) {
-                e.printStackTrace();
-            }
-            sync(context);
-        });
-    }
-
-    public static void enqueueEpisodeAction(Context context, EpisodeAction action) {
-        if (!GpodnetPreferences.loggedIn()) {
-            return;
-        }
-        executeLockedAsync(() -> {
-            try {
-                SharedPreferences prefs = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-                String json = prefs.getString(PREF_QUEUED_EPISODE_ACTIONS, "[]");
-                JSONArray queue = new JSONArray(json);
-                queue.put(action.writeToJsonObject());
-                prefs.edit().putString(PREF_QUEUED_EPISODE_ACTIONS, queue.toString()).apply();
-            } catch (JSONException e) {
-                e.printStackTrace();
+            if (e instanceof SyncServiceException) {
+                if (getRunAttemptCount() % 3 == 2) {
+                    // Do not spam users with notification and retry before notifying
+                    updateErrorNotification(e);
+                }
+                return Result.retry();
+            } else {
+                updateErrorNotification(e);
+                return Result.failure();
             }
-            sync(context);
-        });
-    }
-
-    public static void enqueueEpisodePlayed(Context context, FeedMedia media, boolean completed) {
-        if (!GpodnetPreferences.loggedIn()) {
-            return;
         }
-        if (media.getItem() == null) {
-            return;
-        }
-        if (media.getStartPosition() < 0 || (!completed && media.getStartPosition() >= media.getPosition())) {
-            return;
-        }
-        EpisodeAction action = new EpisodeAction.Builder(media.getItem(), EpisodeAction.PLAY)
-                .currentTimestamp()
-                .started(media.getStartPosition() / 1000)
-                .position((completed ? media.getDuration() : media.getPosition()) / 1000)
-                .total(media.getDuration() / 1000)
-                .build();
-        SyncService.enqueueEpisodeAction(context, action);
     }
 
     public static void sync(Context context) {
@@ -211,13 +116,8 @@ public class SyncService extends Worker {
     }
 
     public static void fullSync(Context context) {
-        executeLockedAsync(() -> {
-            context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                    .putLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0)
-                    .putLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0)
-                    .putLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, 0)
-                    .apply();
-
+        LockingAsyncExecutor.executeLockedAsync(() -> {
+            SynchronizationSettings.resetTimestamps();
             OneTimeWorkRequest workRequest = getWorkRequest()
                     .setInitialDelay(0L, TimeUnit.SECONDS)
                     .build();
@@ -226,108 +126,14 @@ public class SyncService extends Worker {
         });
     }
 
-    private static OneTimeWorkRequest.Builder getWorkRequest() {
-        Constraints.Builder constraints = new Constraints.Builder();
-        if (UserPreferences.isAllowMobileFeedRefresh()) {
-            constraints.setRequiredNetworkType(NetworkType.CONNECTED);
-        } else {
-            constraints.setRequiredNetworkType(NetworkType.UNMETERED);
-        }
-
-        return new OneTimeWorkRequest.Builder(SyncService.class)
-                .setConstraints(constraints.build())
-                .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 10, TimeUnit.MINUTES)
-                .setInitialDelay(5L, TimeUnit.SECONDS); // Give it some time, so other actions can be queued
-    }
-
-    /**
-     * Take the lock and execute runnable (to prevent changes to preferences being lost when enqueueing while sync is
-     * in progress). If the lock is free, the runnable is directly executed in the calling thread to prevent overhead.
-     */
-    private static void executeLockedAsync(Runnable runnable) {
-        if (lock.tryLock()) {
-            try {
-                runnable.run();
-            } finally {
-                lock.unlock();
-            }
-        } else {
-            Completable.fromRunnable(() -> {
-                lock.lock();
-                try {
-                    runnable.run();
-                } finally {
-                    lock.unlock();
-                }
-            }).subscribeOn(Schedulers.io())
-                    .subscribe();
-        }
-    }
-
-    public static boolean isLastSyncSuccessful(Context context) {
-        return context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE)
-                .getBoolean(PREF_LAST_SYNC_ATTEMPT_SUCCESS, false);
-    }
-
-    public static long getLastSyncAttempt(Context context) {
-        return context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE)
-                .getLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, 0);
-    }
-
-    private List<EpisodeAction> getQueuedEpisodeActions() {
-        ArrayList<EpisodeAction> actions = new ArrayList<>();
-        try {
-            SharedPreferences prefs = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-            String json = prefs.getString(PREF_QUEUED_EPISODE_ACTIONS, "[]");
-            JSONArray queue = new JSONArray(json);
-            for (int i = 0; i < queue.length(); i++) {
-                actions.add(EpisodeAction.readFromJsonObject(queue.getJSONObject(i)));
-            }
-        } catch (JSONException e) {
-            e.printStackTrace();
-        }
-        return actions;
-    }
-
-    private List<String> getQueuedRemovedFeeds() {
-        ArrayList<String> actions = new ArrayList<>();
-        try {
-            SharedPreferences prefs = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-            String json = prefs.getString(PREF_QUEUED_FEEDS_REMOVED, "[]");
-            JSONArray queue = new JSONArray(json);
-            for (int i = 0; i < queue.length(); i++) {
-                actions.add(queue.getString(i));
-            }
-        } catch (JSONException e) {
-            e.printStackTrace();
-        }
-        return actions;
-    }
-
-    private List<String> getQueuedAddedFeeds() {
-        ArrayList<String> actions = new ArrayList<>();
-        try {
-            SharedPreferences prefs = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
-            String json = prefs.getString(PREF_QUEUED_FEEDS_ADDED, "[]");
-            JSONArray queue = new JSONArray(json);
-            for (int i = 0; i < queue.length(); i++) {
-                actions.add(queue.getString(i));
-            }
-        } catch (JSONException e) {
-            e.printStackTrace();
-        }
-        return actions;
-    }
-
-    private void syncSubscriptions() throws SyncServiceException {
-        final long lastSync = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE)
-                .getLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0);
+    private void syncSubscriptions(ISyncService syncServiceImpl) throws SyncServiceException {
+        final long lastSync = SynchronizationSettings.getLastSubscriptionSynchronizationTimestamp();
         final List<String> localSubscriptions = DBReader.getFeedListDownloadUrls();
         SubscriptionChanges subscriptionChanges = syncServiceImpl.getSubscriptionChanges(lastSync);
         long newTimeStamp = subscriptionChanges.getTimestamp();
 
-        List<String> queuedRemovedFeeds = getQueuedRemovedFeeds();
-        List<String> queuedAddedFeeds = getQueuedAddedFeeds();
+        List<String> queuedRemovedFeeds = synchronizationQueueStorage.getQueuedRemovedFeeds();
+        List<String> queuedAddedFeeds = synchronizationQueueStorage.getQueuedAddedFeeds();
 
         Log.d(TAG, "Downloaded subscription changes: " + subscriptionChanges);
         for (String downloadUrl : subscriptionChanges.getAdded()) {
@@ -359,26 +165,21 @@ public class SyncService extends Worker {
             Log.d(TAG, "Added: " + StringUtils.join(queuedAddedFeeds, ", "));
             Log.d(TAG, "Removed: " + StringUtils.join(queuedRemovedFeeds, ", "));
 
-            lock.lock();
+            LockingAsyncExecutor.lock.lock();
             try {
                 UploadChangesResponse uploadResponse = syncServiceImpl
                         .uploadSubscriptionChanges(queuedAddedFeeds, queuedRemovedFeeds);
-                getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                        .putString(PREF_QUEUED_FEEDS_ADDED, "[]").apply();
-                getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                        .putString(PREF_QUEUED_FEEDS_REMOVED, "[]").apply();
+                synchronizationQueueStorage.clearFeedQueues();
                 newTimeStamp = uploadResponse.timestamp;
             } finally {
-                lock.unlock();
+                LockingAsyncExecutor.lock.unlock();
             }
         }
-        getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                .putLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, newTimeStamp).apply();
+        SynchronizationSettings.setLastSubscriptionSynchronizationAttemptTimestamp(newTimeStamp);
     }
 
-    private void syncEpisodeActions() throws SyncServiceException {
-        final long lastSync = getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE)
-                .getLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0);
+    private void syncEpisodeActions(ISyncService syncServiceImpl) throws SyncServiceException {
+        final long lastSync = SynchronizationSettings.getLastEpisodeActionSynchronizationTimestamp();
         EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_episodes_download));
         EpisodeActionChanges getResponse = syncServiceImpl.getEpisodeActionChanges(lastSync);
         long newTimeStamp = getResponse.getTimestamp();
@@ -387,7 +188,7 @@ public class SyncService extends Worker {
 
         // upload local actions
         EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_episodes_upload));
-        List<EpisodeAction> queuedEpisodeActions = getQueuedEpisodeActions();
+        List<EpisodeAction> queuedEpisodeActions = synchronizationQueueStorage.getQueuedEpisodeActions();
         if (lastSync == 0) {
             EventBus.getDefault().postSticky(new SyncServiceEvent(R.string.sync_status_upload_played));
             List<FeedItem> readItems = DBReader.getPlayedItems();
@@ -407,24 +208,21 @@ public class SyncService extends Worker {
             }
         }
         if (queuedEpisodeActions.size() > 0) {
-            lock.lock();
+            LockingAsyncExecutor.lock.lock();
             try {
                 Log.d(TAG, "Uploading " + queuedEpisodeActions.size() + " actions: "
                         + StringUtils.join(queuedEpisodeActions, ", "));
                 UploadChangesResponse postResponse = syncServiceImpl.uploadEpisodeActions(queuedEpisodeActions);
                 newTimeStamp = postResponse.timestamp;
                 Log.d(TAG, "Upload episode response: " + postResponse);
-                getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                        .putString(PREF_QUEUED_EPISODE_ACTIONS, "[]").apply();
+                synchronizationQueueStorage.clearEpisodeActionQueue();
             } finally {
-                lock.unlock();
+                LockingAsyncExecutor.lock.unlock();
             }
         }
-        getApplicationContext().getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                .putLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, newTimeStamp).apply();
+        SynchronizationSettings.setLastEpisodeActionSynchronizationAttemptTimestamp(newTimeStamp);
     }
 
-
     private synchronized void processEpisodeActions(List<EpisodeAction> remoteActions) {
         Log.d(TAG, "Processing " + remoteActions.size() + " actions");
         if (remoteActions.size() == 0) {
@@ -432,7 +230,8 @@ public class SyncService extends Worker {
         }
 
         Map<Pair<String, String>, EpisodeAction> playActionsToUpdate = EpisodeActionFilter
-                .getRemoteActionsOverridingLocalActions(remoteActions, getQueuedEpisodeActions());
+                .getRemoteActionsOverridingLocalActions(remoteActions,
+                        synchronizationQueueStorage.getQueuedEpisodeActions());
         LongList queueToBeRemoved = new LongList();
         List<FeedItem> updatedItems = new ArrayList<>();
         for (EpisodeAction action : playActionsToUpdate.values()) {
@@ -442,20 +241,24 @@ public class SyncService extends Worker {
                 Log.i(TAG, "Unknown feed item: " + action);
                 continue;
             }
+            if (feedItem.getMedia() == null) {
+                Log.i(TAG, "Feed item has no media: " + action);
+                continue;
+            }
             if (action.getAction() == EpisodeAction.NEW) {
                 DBWriter.markItemPlayed(feedItem, FeedItem.UNPLAYED, true);
                 continue;
             }
-            Log.d(TAG, "Most recent play action: " + action.toString());
-            FeedMedia media = feedItem.getMedia();
-            media.setPosition(action.getPosition() * 1000);
+            feedItem.getMedia().setPosition(action.getPosition() * 1000);
             if (FeedItemUtil.hasAlmostEnded(feedItem.getMedia())) {
-                Log.d(TAG, "Marking as played");
+                Log.d(TAG, "Marking as played: " + action);
                 feedItem.setPlayed(true);
+                feedItem.getMedia().setPosition(0);
                 queueToBeRemoved.add(feedItem.getId());
+            } else {
+                Log.d(TAG, "Setting position: " + action);
             }
             updatedItems.add(feedItem);
-
         }
         DBWriter.removeQueueItem(getApplicationContext(), false, queueToBeRemoved.toArray());
         DBReader.loadAdditionalFeedItemListData(updatedItems);
@@ -469,7 +272,7 @@ public class SyncService extends Worker {
         nm.cancel(R.id.notification_gpodnet_sync_autherror);
     }
 
-    private void updateErrorNotification(SyncServiceException exception) {
+    private void updateErrorNotification(Exception exception) {
         if (!UserPreferences.gpodnetNotificationsEnabled()) {
             Log.d(TAG, "Skipping sync error notification because of user setting");
             return;
@@ -486,6 +289,7 @@ public class SyncService extends Worker {
                 NotificationUtils.CHANNEL_ID_SYNC_ERROR)
                 .setContentTitle(getApplicationContext().getString(R.string.gpodnetsync_error_title))
                 .setContentText(description)
+                .setStyle(new NotificationCompat.BigTextStyle().bigText(description))
                 .setContentIntent(pendingIntent)
                 .setSmallIcon(R.drawable.ic_notification_sync_error)
                 .setAutoCancel(true)
@@ -495,4 +299,36 @@ public class SyncService extends Worker {
                 .getSystemService(Context.NOTIFICATION_SERVICE);
         nm.notify(R.id.notification_gpodnet_sync_error, notification);
     }
+
+    private static OneTimeWorkRequest.Builder getWorkRequest() {
+        Constraints.Builder constraints = new Constraints.Builder();
+        if (UserPreferences.isAllowMobileFeedRefresh()) {
+            constraints.setRequiredNetworkType(NetworkType.CONNECTED);
+        } else {
+            constraints.setRequiredNetworkType(NetworkType.UNMETERED);
+        }
+
+        return new OneTimeWorkRequest.Builder(SyncService.class)
+                .setConstraints(constraints.build())
+                .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 10, TimeUnit.MINUTES)
+                .setInitialDelay(5L, TimeUnit.SECONDS); // Give it some time, so other actions can be queued
+    }
+
+    private ISyncService getActiveSyncProvider() {
+        String selectedSyncProviderKey = SynchronizationSettings.getSelectedSyncProviderKey();
+        SynchronizationProviderViewData selectedService = SynchronizationProviderViewData
+                .valueOf(selectedSyncProviderKey);
+        switch (selectedService) {
+            case GPODDER_NET:
+                return new GpodnetService(AntennapodHttpClient.getHttpClient(),
+                        SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getDeviceID(),
+                        SynchronizationCredentials.getUsername(), SynchronizationCredentials.getPassword());
+            case NEXTCLOUD_GPODDER:
+                return new NextcloudSyncService(AntennapodHttpClient.getHttpClient(),
+                        SynchronizationCredentials.getHosturl(), SynchronizationCredentials.getUsername(),
+                        SynchronizationCredentials.getPassword());
+            default:
+                return null;
+        }
+    }
 }
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationCredentials.java b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationCredentials.java
new file mode 100644
index 000000000..e08bc66ad
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationCredentials.java
@@ -0,0 +1,67 @@
+package de.danoeh.antennapod.core.sync;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import de.danoeh.antennapod.core.ClientConfig;
+import de.danoeh.antennapod.core.preferences.UserPreferences;
+import de.danoeh.antennapod.core.sync.queue.SynchronizationQueueSink;
+
+/**
+ * Manages preferences for accessing gpodder.net service and other sync providers
+ */
+public class SynchronizationCredentials {
+
+    private SynchronizationCredentials() {
+    }
+
+    private static final String PREF_NAME = "gpodder.net";
+    private static final String PREF_USERNAME = "de.danoeh.antennapod.preferences.gpoddernet.username";
+    private static final String PREF_PASSWORD = "de.danoeh.antennapod.preferences.gpoddernet.password";
+    private static final String PREF_DEVICEID = "de.danoeh.antennapod.preferences.gpoddernet.deviceID";
+    private static final String PREF_HOSTNAME = "prefGpodnetHostname";
+
+    private static SharedPreferences getPreferences() {
+        return ClientConfig.applicationCallbacks.getApplicationInstance()
+                .getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
+    }
+
+    public static String getUsername() {
+        return getPreferences().getString(PREF_USERNAME, null);
+    }
+
+    public static void setUsername(String username) {
+        getPreferences().edit().putString(PREF_USERNAME, username).apply();
+    }
+
+    public static String getPassword() {
+        return getPreferences().getString(PREF_PASSWORD, null);
+    }
+
+    public static void setPassword(String password) {
+        getPreferences().edit().putString(PREF_PASSWORD, password).apply();
+    }
+
+    public static String getDeviceID() {
+        return getPreferences().getString(PREF_DEVICEID, null);
+    }
+
+    public static void setDeviceID(String deviceID) {
+        getPreferences().edit().putString(PREF_DEVICEID, deviceID).apply();
+    }
+
+    public static String getHosturl() {
+        return getPreferences().getString(PREF_HOSTNAME, null);
+    }
+
+    public static void setHosturl(String value) {
+        getPreferences().edit().putString(PREF_HOSTNAME, value).apply();
+    }
+
+    public static synchronized void clear(Context context) {
+        setUsername(null);
+        setPassword(null);
+        setDeviceID(null);
+        SynchronizationQueueSink.clearQueue(context);
+        UserPreferences.setGpodnetNotificationsEnabled();
+    }
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationProviderViewData.java b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationProviderViewData.java
new file mode 100644
index 000000000..cba713f60
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationProviderViewData.java
@@ -0,0 +1,47 @@
+package de.danoeh.antennapod.core.sync;
+
+import de.danoeh.antennapod.core.R;
+
+public enum SynchronizationProviderViewData {
+    GPODDER_NET(
+            "GPODDER_NET",
+            R.string.gpodnet_description,
+            R.drawable.gpodder_icon
+    ),
+    NEXTCLOUD_GPODDER(
+            "NEXTCLOUD_GPODDER",
+            R.string.synchronization_summary_nextcloud,
+            R.drawable.nextcloud_logo
+    );
+
+    public static SynchronizationProviderViewData fromIdentifier(String provider) {
+        for (SynchronizationProviderViewData synchronizationProvider : SynchronizationProviderViewData.values()) {
+            if (synchronizationProvider.getIdentifier().equals(provider)) {
+                return synchronizationProvider;
+            }
+        }
+        return null;
+    }
+
+    private final String identifier;
+    private final int iconResource;
+    private final int summaryResource;
+
+    SynchronizationProviderViewData(String identifier, int summaryResource, int iconResource) {
+        this.identifier = identifier;
+        this.iconResource = iconResource;
+        this.summaryResource = summaryResource;
+    }
+
+    public String getIdentifier() {
+        return identifier;
+    }
+
+    public int getIconResource() {
+        return iconResource;
+    }
+
+    public int getSummaryResource() {
+        return summaryResource;
+    }
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationSettings.java b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationSettings.java
new file mode 100644
index 000000000..1a53ac0fb
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/SynchronizationSettings.java
@@ -0,0 +1,83 @@
+package de.danoeh.antennapod.core.sync;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+
+import de.danoeh.antennapod.core.ClientConfig;
+
+public class SynchronizationSettings {
+
+    public static final String LAST_SYNC_ATTEMPT_TIMESTAMP = "last_sync_attempt_timestamp";
+    private static final String NAME = "synchronization";
+    private static final String SELECTED_SYNC_PROVIDER = "selected_sync_provider";
+    private static final String LAST_SYNC_ATTEMPT_SUCCESS = "last_sync_attempt_success";
+    private static final String LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP = "last_episode_actions_sync_timestamp";
+    private static final String LAST_SUBSCRIPTION_SYNC_TIMESTAMP = "last_sync_timestamp";
+
+    public static boolean isProviderConnected() {
+        return getSelectedSyncProviderKey() != null;
+    }
+
+    public static void resetTimestamps() {
+        getSharedPreferences().edit()
+                .putLong(LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0)
+                .putLong(LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0)
+                .putLong(LAST_SYNC_ATTEMPT_TIMESTAMP, 0)
+                .apply();
+    }
+
+    public static boolean isLastSyncSuccessful() {
+        return getSharedPreferences().getBoolean(LAST_SYNC_ATTEMPT_SUCCESS, false);
+    }
+
+    public static long getLastSyncAttempt() {
+        return getSharedPreferences().getLong(LAST_SYNC_ATTEMPT_TIMESTAMP, 0);
+    }
+
+    public static void setSelectedSyncProvider(SynchronizationProviderViewData provider) {
+        getSharedPreferences()
+                .edit()
+                .putString(SELECTED_SYNC_PROVIDER, provider == null ? null : provider.getIdentifier())
+                .apply();
+    }
+
+    public static String getSelectedSyncProviderKey() {
+        return getSharedPreferences().getString(SELECTED_SYNC_PROVIDER, null);
+    }
+
+    public static void updateLastSynchronizationAttempt() {
+        getSharedPreferences().edit()
+                .putLong(LAST_SYNC_ATTEMPT_TIMESTAMP, System.currentTimeMillis())
+                .apply();
+    }
+
+    public static void setLastSynchronizationAttemptSuccess(boolean isSuccess) {
+        getSharedPreferences().edit()
+                .putBoolean(LAST_SYNC_ATTEMPT_SUCCESS, isSuccess)
+                .apply();
+    }
+
+    public static long getLastSubscriptionSynchronizationTimestamp() {
+        return getSharedPreferences().getLong(LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0);
+    }
+
+    public static void setLastSubscriptionSynchronizationAttemptTimestamp(long newTimeStamp) {
+        getSharedPreferences().edit()
+                .putLong(LAST_SUBSCRIPTION_SYNC_TIMESTAMP, newTimeStamp).apply();
+    }
+
+    public static long getLastEpisodeActionSynchronizationTimestamp() {
+        return getSharedPreferences()
+                .getLong(LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0);
+    }
+
+    public static void setLastEpisodeActionSynchronizationAttemptTimestamp(long timestamp) {
+        getSharedPreferences().edit()
+                .putLong(LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, timestamp).apply();
+    }
+
+    private static SharedPreferences getSharedPreferences() {
+        return ClientConfig.applicationCallbacks.getApplicationInstance()
+                .getSharedPreferences(NAME, Context.MODE_PRIVATE);
+    }
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueSink.java b/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueSink.java
new file mode 100644
index 000000000..445faf60f
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueSink.java
@@ -0,0 +1,67 @@
+package de.danoeh.antennapod.core.sync.queue;
+
+import android.content.Context;
+
+import de.danoeh.antennapod.core.sync.LockingAsyncExecutor;
+import de.danoeh.antennapod.core.sync.SyncService;
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
+import de.danoeh.antennapod.model.feed.FeedMedia;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+
+public class SynchronizationQueueSink {
+
+    public static void clearQueue(Context context) {
+        LockingAsyncExecutor.executeLockedAsync(new SynchronizationQueueStorage(context)::clearQueue);
+    }
+
+    public static void enqueueFeedAddedIfSynchronizationIsActive(Context context, String downloadUrl) {
+        if (!SynchronizationSettings.isProviderConnected()) {
+            return;
+        }
+        LockingAsyncExecutor.executeLockedAsync(() -> {
+            new SynchronizationQueueStorage(context).enqueueFeedAdded(downloadUrl);
+            SyncService.sync(context);
+        });
+    }
+
+    public static void enqueueFeedRemovedIfSynchronizationIsActive(Context context, String downloadUrl) {
+        if (!SynchronizationSettings.isProviderConnected()) {
+            return;
+        }
+        LockingAsyncExecutor.executeLockedAsync(() -> {
+            new SynchronizationQueueStorage(context).enqueueFeedRemoved(downloadUrl);
+            SyncService.sync(context);
+        });
+    }
+
+    public static void enqueueEpisodeActionIfSynchronizationIsActive(Context context, EpisodeAction action) {
+        if (!SynchronizationSettings.isProviderConnected()) {
+            return;
+        }
+        LockingAsyncExecutor.executeLockedAsync(() -> {
+            new SynchronizationQueueStorage(context).enqueueEpisodeAction(action);
+            SyncService.sync(context);
+        });
+    }
+
+    public static void enqueueEpisodePlayedIfSynchronizationIsActive(Context context, FeedMedia media,
+                                                                     boolean completed) {
+        if (!SynchronizationSettings.isProviderConnected()) {
+            return;
+        }
+        if (media.getItem() == null) {
+            return;
+        }
+        if (media.getStartPosition() < 0 || (!completed && media.getStartPosition() >= media.getPosition())) {
+            return;
+        }
+        EpisodeAction action = new EpisodeAction.Builder(media.getItem(), EpisodeAction.PLAY)
+                .currentTimestamp()
+                .started(media.getStartPosition() / 1000)
+                .position((completed ? media.getDuration() : media.getPosition()) / 1000)
+                .total(media.getDuration() / 1000)
+                .build();
+        enqueueEpisodeActionIfSynchronizationIsActive(context, action);
+    }
+
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueStorage.java b/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueStorage.java
new file mode 100644
index 000000000..5c6d58fe3
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/queue/SynchronizationQueueStorage.java
@@ -0,0 +1,140 @@
+package de.danoeh.antennapod.core.sync.queue;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+
+import java.util.ArrayList;
+
+import de.danoeh.antennapod.core.sync.SynchronizationSettings;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+
+public class SynchronizationQueueStorage {
+
+    private static final String NAME = "synchronization";
+    private static final String QUEUED_EPISODE_ACTIONS = "sync_queued_episode_actions";
+    private static final String QUEUED_FEEDS_REMOVED = "sync_removed";
+    private static final String QUEUED_FEEDS_ADDED = "sync_added";
+    private final SharedPreferences sharedPreferences;
+
+    public SynchronizationQueueStorage(Context context) {
+        this.sharedPreferences = context.getSharedPreferences(NAME, Context.MODE_PRIVATE);
+    }
+
+    public ArrayList<EpisodeAction> getQueuedEpisodeActions() {
+        ArrayList<EpisodeAction> actions = new ArrayList<>();
+        try {
+            String json = getSharedPreferences()
+                    .getString(QUEUED_EPISODE_ACTIONS, "[]");
+            JSONArray queue = new JSONArray(json);
+            for (int i = 0; i < queue.length(); i++) {
+                actions.add(EpisodeAction.readFromJsonObject(queue.getJSONObject(i)));
+            }
+        } catch (JSONException e) {
+            e.printStackTrace();
+        }
+        return actions;
+    }
+
+    public ArrayList<String> getQueuedRemovedFeeds() {
+        ArrayList<String> removedFeedUrls = new ArrayList<>();
+        try {
+            String json = getSharedPreferences()
+                    .getString(QUEUED_FEEDS_REMOVED, "[]");
+            JSONArray queue = new JSONArray(json);
+            for (int i = 0; i < queue.length(); i++) {
+                removedFeedUrls.add(queue.getString(i));
+            }
+        } catch (JSONException e) {
+            e.printStackTrace();
+        }
+        return removedFeedUrls;
+
+    }
+
+    public ArrayList<String> getQueuedAddedFeeds() {
+        ArrayList<String> addedFeedUrls = new ArrayList<>();
+        try {
+            String json = getSharedPreferences()
+                    .getString(QUEUED_FEEDS_ADDED, "[]");
+            JSONArray queue = new JSONArray(json);
+            for (int i = 0; i < queue.length(); i++) {
+                addedFeedUrls.add(queue.getString(i));
+            }
+        } catch (JSONException e) {
+            e.printStackTrace();
+        }
+        return addedFeedUrls;
+    }
+
+    public void clearEpisodeActionQueue() {
+        getSharedPreferences().edit()
+                .putString(QUEUED_EPISODE_ACTIONS, "[]").apply();
+
+    }
+
+    public void clearFeedQueues() {
+        getSharedPreferences().edit()
+                .putString(QUEUED_FEEDS_ADDED, "[]")
+                .putString(QUEUED_FEEDS_REMOVED, "[]")
+                .apply();
+    }
+
+    protected void clearQueue() {
+        SynchronizationSettings.resetTimestamps();
+        getSharedPreferences().edit()
+                .putString(QUEUED_EPISODE_ACTIONS, "[]")
+                .putString(QUEUED_FEEDS_ADDED, "[]")
+                .putString(QUEUED_FEEDS_REMOVED, "[]")
+                .apply();
+
+    }
+
+    protected void enqueueFeedAdded(String downloadUrl) {
+        SharedPreferences sharedPreferences = getSharedPreferences();
+        String json = sharedPreferences
+                .getString(QUEUED_FEEDS_ADDED, "[]");
+        try {
+            JSONArray queue = new JSONArray(json);
+            queue.put(downloadUrl);
+            sharedPreferences
+                    .edit().putString(QUEUED_FEEDS_ADDED, queue.toString()).apply();
+
+        } catch (JSONException jsonException) {
+            jsonException.printStackTrace();
+        }
+    }
+
+    protected void enqueueFeedRemoved(String downloadUrl) {
+        SharedPreferences sharedPreferences = getSharedPreferences();
+        String json = sharedPreferences.getString(QUEUED_FEEDS_REMOVED, "[]");
+        try {
+            JSONArray queue = new JSONArray(json);
+            queue.put(downloadUrl);
+            sharedPreferences.edit().putString(QUEUED_FEEDS_REMOVED, queue.toString())
+                    .apply();
+        } catch (JSONException jsonException) {
+            jsonException.printStackTrace();
+        }
+    }
+
+    protected void enqueueEpisodeAction(EpisodeAction action) {
+        SharedPreferences sharedPreferences = getSharedPreferences();
+        String json = sharedPreferences.getString(QUEUED_EPISODE_ACTIONS, "[]");
+        try {
+            JSONArray queue = new JSONArray(json);
+            queue.put(action.writeToJsonObject());
+            sharedPreferences.edit().putString(
+                    QUEUED_EPISODE_ACTIONS, queue.toString()
+            ).apply();
+        } catch (JSONException jsonException) {
+            jsonException.printStackTrace();
+        }
+    }
+
+    private SharedPreferences getSharedPreferences() {
+        return sharedPreferences;
+    }
+}
diff --git a/core/src/main/res/drawable-nodpi/nextcloud_logo.png b/core/src/main/res/drawable-nodpi/nextcloud_logo.png
new file mode 100644
index 000000000..2164e37fb
--- /dev/null
+++ b/core/src/main/res/drawable-nodpi/nextcloud_logo.png
diff --git a/core/src/main/res/values/strings.xml b/core/src/main/res/values/strings.xml
index 5f509a9b6..7aa32abe3 100644
--- a/core/src/main/res/values/strings.xml
+++ b/core/src/main/res/values/strings.xml
@@ -356,7 +356,7 @@
     <string name="storage_sum">Episode auto delete, Import, Export</string>
     <string name="project_pref">Project</string>
     <string name="synchronization_pref">Synchronization</string>
-    <string name="synchronization_sum">Synchronize with other devices using gpodder.net</string>
+    <string name="synchronization_sum">Synchronize with other devices</string>
     <string name="automation">Automation</string>
     <string name="download_pref_details">Details</string>
     <string name="import_export_pref">Import/Export</string>
@@ -447,17 +447,20 @@
     <string name="pref_theme_title_dark">Dark</string>
     <string name="pref_theme_title_trueblack">Black (AMOLED ready)</string>
     <string name="pref_episode_cache_unlimited">Unlimited</string>
-    <string name="pref_gpodnet_authenticate_title">Login</string>
-    <string name="pref_gpodnet_authenticate_sum">Login with your gpodder.net account in order to sync your subscriptions.</string>
-    <string name="pref_gpodnet_logout_title">Logout</string>
-    <string name="pref_gpodnet_logout_toast">Logout was successful</string>
+    <string name="synchronization_logout">Logout</string>
+    <string name="pref_synchronization_logout_toast">Logout was successful</string>
     <string name="pref_gpodnet_setlogin_information_title">Change login information</string>
     <string name="pref_gpodnet_setlogin_information_sum">Change the login information for your gpodder.net account.</string>
-    <string name="pref_gpodnet_sync_changes_title">Synchronize now</string>
-    <string name="pref_gpodnet_sync_changes_sum">Sync subscription and episode state changes with gpodder.net.</string>
-    <string name="pref_gpodnet_full_sync_title">Force full synchronization</string>
-    <string name="pref_gpodnet_full_sync_sum">Sync all subscriptions and episode states with gpodder.net.</string>
-    <string name="pref_gpodnet_login_status"><![CDATA[Logged in as <i>%1$s</i> with device <i>%2$s</i>]]></string>
+    <string name="synchronization_sync_changes_title">Synchronize now</string>
+    <string name="synchronization_full_sync_title">Force full synchronization</string>
+    <string name="synchronization_login_status"><![CDATA[Logged in as <i>%1$s</i> on <i>%2$s</i>. <br/><br/>You can choose your synchronization provider again once you have logged out]]></string>
+    <string name="synchronization_summary_unchoosen">You can choose from multiple providers to synchronize your subscriptions and episode play state with</string>
+    <string name="synchronization_summary_nextcloud">Gpoddersync is an open-source Nextcloud app that you can easily install on your own server. The app is independent of the AntennaPod project.</string>
+    <string name="synchronization_nextcloud_authenticate_browser">Grant access using the opened web browser and come back to AntennaPod.</string>
+    <string name="synchronization_choose_title">Choose synchronization provider</string>
+    <string name="synchronization_force_sync_summary">Re-synchronize all subscriptions and episode states</string>
+    <string name="synchronization_sync_summary">Synchronize subscription and episode state changes</string>
+    <string name="dialog_choose_sync_service_title">Choose synchronization provider</string>
     <string name="pref_playback_speed_sum">Customize the speeds available for variable speed playback</string>
     <string name="pref_feed_playback_speed_sum">The speed to use when starting audio playback for episodes in this podcast</string>
     <string name="pref_feed_skip">Auto Skip</string>
diff --git a/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java b/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java
index 356a7f77e..552f7d70a 100644
--- a/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java
+++ b/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java
@@ -14,5 +14,6 @@ public class GuidValidatorTest extends TestCase {
         assertFalse(GuidValidator.isValidGuid("\n"));
         assertFalse(GuidValidator.isValidGuid(" \n"));
         assertFalse(GuidValidator.isValidGuid(null));
+        assertFalse(GuidValidator.isValidGuid("null"));
     }
 }
\ No newline at end of file
diff --git a/net/sync/gpoddernet/build.gradle b/net/sync/gpoddernet/build.gradle
index eb5af1b60..77e9ce0f3 100644
--- a/net/sync/gpoddernet/build.gradle
+++ b/net/sync/gpoddernet/build.gradle
@@ -9,4 +9,7 @@ dependencies {
 
     implementation "com.squareup.okhttp3:okhttp:$okhttpVersion"
     implementation "org.apache.commons:commons-lang3:$commonslangVersion"
+    implementation 'commons-io:commons-io:2.5'
+    implementation "io.reactivex.rxjava2:rxandroid:$rxAndroidVersion"
+    implementation "io.reactivex.rxjava2:rxjava:$rxJavaVersion"
 }
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/HostnameParser.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/HostnameParser.java
new file mode 100644
index 000000000..ebb415248
--- /dev/null
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/HostnameParser.java
@@ -0,0 +1,41 @@
+package de.danoeh.antennapod.net.sync;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class HostnameParser {
+    public String scheme;
+    public int port;
+    public String host;
+
+    // split into schema, host and port - missing parts are null
+    private static final Pattern URLSPLIT_REGEX = Pattern.compile("(?:(https?)://)?([^:]+)(?::(\\d+))?");
+
+    public HostnameParser(String hosturl) {
+        Matcher m = URLSPLIT_REGEX.matcher(hosturl);
+        if (m.matches()) {
+            scheme = m.group(1);
+            host = m.group(2);
+            if (m.group(3) == null) {
+                port = -1;
+            } else {
+                port = Integer.parseInt(m.group(3));    // regex -> can only be digits
+            }
+        } else {
+            // URL does not match regex: use it anyway -> this will cause an exception on connect
+            scheme = "https";
+            host = hosturl;
+            port = 443;
+        }
+
+        if (scheme == null) {      // assume https
+            scheme = "https";
+        }
+
+        if (scheme.equals("https") && port == -1) {
+            port = 443;
+        } else if (scheme.equals("http") && port == -1) {
+            port = 80;
+        }
+    }
+}
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/GpodnetService.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/GpodnetService.java
index eb18da80b..439a528b7 100644
--- a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/GpodnetService.java
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/GpodnetService.java
@@ -1,25 +1,10 @@
 package de.danoeh.antennapod.net.sync.gpoddernet;
 
 import android.util.Log;
+
 import androidx.annotation.NonNull;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetDevice;
-import de.danoeh.antennapod.net.sync.model.EpisodeAction;
-import de.danoeh.antennapod.net.sync.model.EpisodeActionChanges;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetEpisodeActionPostResponse;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetPodcast;
-import de.danoeh.antennapod.net.sync.model.ISyncService;
-import de.danoeh.antennapod.net.sync.model.SubscriptionChanges;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetTag;
-import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetUploadChangesResponse;
-import de.danoeh.antennapod.net.sync.model.SyncServiceException;
-import de.danoeh.antennapod.net.sync.model.UploadChangesResponse;
-import okhttp3.Credentials;
-import okhttp3.MediaType;
-import okhttp3.OkHttpClient;
-import okhttp3.Request;
-import okhttp3.RequestBody;
-import okhttp3.Response;
-import okhttp3.ResponseBody;
+
+import de.danoeh.antennapod.net.sync.HostnameParser;
 import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -35,12 +20,28 @@ import java.net.URL;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
 
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
+import de.danoeh.antennapod.net.sync.gpoddernet.mapper.ResponseMapper;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetDevice;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetEpisodeActionPostResponse;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetPodcast;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetTag;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetUploadChangesResponse;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+import de.danoeh.antennapod.net.sync.model.EpisodeActionChanges;
+import de.danoeh.antennapod.net.sync.model.ISyncService;
+import de.danoeh.antennapod.net.sync.model.SubscriptionChanges;
+import de.danoeh.antennapod.net.sync.model.SyncServiceException;
+import de.danoeh.antennapod.net.sync.model.UploadChangesResponse;
+import okhttp3.Credentials;
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.RequestBody;
+import okhttp3.Response;
+import okhttp3.ResponseBody;
 
 /**
  * Communicates with the gpodder.net service.
@@ -61,43 +62,16 @@ public class GpodnetService implements ISyncService {
 
     private final OkHttpClient httpClient;
 
-    // split into schema, host and port - missing parts are null
-    private static final Pattern URLSPLIT_REGEX = Pattern.compile("(?:(https?)://)?([^:]+)(?::(\\d+))?");
-
     public GpodnetService(OkHttpClient httpClient, String baseHosturl,
                           String deviceId, String username, String password)  {
         this.httpClient = httpClient;
         this.deviceId = deviceId;
         this.username = username;
         this.password = password;
-
-        Matcher m = URLSPLIT_REGEX.matcher(baseHosturl);
-        if (m.matches()) {
-            this.baseScheme = m.group(1);
-            this.baseHost = m.group(2);
-            if (m.group(3) == null) {
-                this.basePort = -1;
-            } else {
-                this.basePort = Integer.parseInt(m.group(3));    // regex -> can only be digits
-            }
-        } else {
-            // URL does not match regex: use it anyway -> this will cause an exception on connect
-            this.baseScheme = "https";
-            this.baseHost = baseHosturl;
-            this.basePort = 443;
-        }
-
-        if (this.baseScheme == null) {      // assume https
-            this.baseScheme = "https";
-        }
-
-        if (this.baseScheme.equals("https") && this.basePort == -1) {
-            this.basePort = 443;
-        }
-
-        if (this.baseScheme.equals("http") && this.basePort == -1) {
-            this.basePort = 80;
-        }
+        HostnameParser hostname = new HostnameParser(baseHosturl == null ? DEFAULT_BASE_HOST : baseHosturl);
+        this.baseHost = hostname.host;
+        this.basePort = hostname.port;
+        this.baseScheme = hostname.scheme;
     }
 
     private void requireLoggedIn() {
@@ -434,7 +408,7 @@ public class GpodnetService implements ISyncService {
 
             String response = executeRequest(request);
             JSONObject changes = new JSONObject(response);
-            return readSubscriptionChangesFromJsonObject(changes);
+            return ResponseMapper.readSubscriptionChangesFromJsonObject(changes);
         } catch (URISyntaxException e) {
             e.printStackTrace();
             throw new IllegalStateException(e);
@@ -515,7 +489,7 @@ public class GpodnetService implements ISyncService {
 
             String response = executeRequest(request);
             JSONObject json = new JSONObject(response);
-            return readEpisodeActionsFromJsonObject(json);
+            return ResponseMapper.readEpisodeActionsFromJsonObject(json);
         } catch (URISyntaxException e) {
             e.printStackTrace();
             throw new IllegalStateException(e);
@@ -526,7 +500,6 @@ public class GpodnetService implements ISyncService {
 
     }
 
-
     /**
      * Logs in a specific user. This method must be called if any of the methods
      * that require authentication is used.
@@ -689,48 +662,6 @@ public class GpodnetService implements ISyncService {
         return new GpodnetDevice(id, caption, type, subscriptions);
     }
 
-    private SubscriptionChanges readSubscriptionChangesFromJsonObject(@NonNull JSONObject object)
-            throws JSONException {
-
-        List<String> added = new LinkedList<>();
-        JSONArray jsonAdded = object.getJSONArray("add");
-        for (int i = 0; i < jsonAdded.length(); i++) {
-            String addedUrl = jsonAdded.getString(i);
-            // gpodder escapes colons unnecessarily
-            addedUrl = addedUrl.replace("%3A", ":");
-            added.add(addedUrl);
-        }
-
-        List<String> removed = new LinkedList<>();
-        JSONArray jsonRemoved = object.getJSONArray("remove");
-        for (int i = 0; i < jsonRemoved.length(); i++) {
-            String removedUrl = jsonRemoved.getString(i);
-            // gpodder escapes colons unnecessarily
-            removedUrl = removedUrl.replace("%3A", ":");
-            removed.add(removedUrl);
-        }
-
-        long timestamp = object.getLong("timestamp");
-        return new SubscriptionChanges(added, removed, timestamp);
-    }
-
-    private EpisodeActionChanges readEpisodeActionsFromJsonObject(@NonNull JSONObject object)
-            throws JSONException {
-
-        List<EpisodeAction> episodeActions = new ArrayList<>();
-
-        long timestamp = object.getLong("timestamp");
-        JSONArray jsonActions = object.getJSONArray("actions");
-        for (int i = 0; i < jsonActions.length(); i++) {
-            JSONObject jsonAction = jsonActions.getJSONObject(i);
-            EpisodeAction episodeAction = EpisodeAction.readFromJsonObject(jsonAction);
-            if (episodeAction != null) {
-                episodeActions.add(episodeAction);
-            }
-        }
-        return new EpisodeActionChanges(episodeActions, timestamp);
-    }
-
     @Override
     public void logout() {
 
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/mapper/ResponseMapper.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/mapper/ResponseMapper.java
new file mode 100644
index 000000000..c8e607d74
--- /dev/null
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/gpoddernet/mapper/ResponseMapper.java
@@ -0,0 +1,60 @@
+package de.danoeh.antennapod.net.sync.gpoddernet.mapper;
+
+import androidx.annotation.NonNull;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+import de.danoeh.antennapod.net.sync.model.EpisodeActionChanges;
+import de.danoeh.antennapod.net.sync.model.SubscriptionChanges;
+
+public class ResponseMapper {
+
+    public static SubscriptionChanges readSubscriptionChangesFromJsonObject(@NonNull JSONObject object)
+            throws JSONException {
+
+        List<String> added = new LinkedList<>();
+        JSONArray jsonAdded = object.getJSONArray("add");
+        for (int i = 0; i < jsonAdded.length(); i++) {
+            String addedUrl = jsonAdded.getString(i);
+            // gpodder escapes colons unnecessarily
+            addedUrl = addedUrl.replace("%3A", ":");
+            added.add(addedUrl);
+        }
+
+        List<String> removed = new LinkedList<>();
+        JSONArray jsonRemoved = object.getJSONArray("remove");
+        for (int i = 0; i < jsonRemoved.length(); i++) {
+            String removedUrl = jsonRemoved.getString(i);
+            // gpodder escapes colons unnecessarily
+            removedUrl = removedUrl.replace("%3A", ":");
+            removed.add(removedUrl);
+        }
+
+        long timestamp = object.getLong("timestamp");
+        return new SubscriptionChanges(added, removed, timestamp);
+    }
+
+    public static EpisodeActionChanges readEpisodeActionsFromJsonObject(@NonNull JSONObject object)
+            throws JSONException {
+
+        List<EpisodeAction> episodeActions = new ArrayList<>();
+
+        long timestamp = object.getLong("timestamp");
+        JSONArray jsonActions = object.getJSONArray("actions");
+        for (int i = 0; i < jsonActions.length(); i++) {
+            JSONObject jsonAction = jsonActions.getJSONObject(i);
+            EpisodeAction episodeAction = EpisodeAction.readFromJsonObject(jsonAction);
+            if (episodeAction != null) {
+                episodeActions.add(episodeAction);
+            }
+        }
+        return new EpisodeActionChanges(episodeActions, timestamp);
+    }
+}
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudLoginFlow.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudLoginFlow.java
new file mode 100644
index 000000000..b66c44402
--- /dev/null
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudLoginFlow.java
@@ -0,0 +1,107 @@
+package de.danoeh.antennapod.net.sync.nextcloud;
+
+import android.content.Context;
+import android.content.Intent;
+import android.net.Uri;
+import de.danoeh.antennapod.net.sync.HostnameParser;
+import io.reactivex.Observable;
+import io.reactivex.android.schedulers.AndroidSchedulers;
+import io.reactivex.disposables.Disposable;
+import io.reactivex.schedulers.Schedulers;
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.RequestBody;
+import okhttp3.Response;
+import okhttp3.ResponseBody;
+import org.json.JSONException;
+import org.json.JSONObject;
+import android.util.Log;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.URL;
+import java.util.concurrent.TimeUnit;
+
+public class NextcloudLoginFlow {
+    private static final String TAG = "NextcloudLoginFlow";
+
+    private final OkHttpClient httpClient;
+    private final HostnameParser hostname;
+    private final Context context;
+    private final AuthenticationCallback callback;
+    private String token;
+    private String endpoint;
+    private Disposable startDisposable;
+    private Disposable pollDisposable;
+
+    public NextcloudLoginFlow(OkHttpClient httpClient, String hostUrl, Context context,
+                              AuthenticationCallback callback) {
+        this.httpClient = httpClient;
+        this.hostname = new HostnameParser(hostUrl);
+        this.context = context;
+        this.callback = callback;
+    }
+
+    public void start() {
+        startDisposable = Observable.fromCallable(() -> {
+            URL url = new URI(hostname.scheme, null, hostname.host, hostname.port,
+                    "/index.php/login/v2", null, null).toURL();
+            JSONObject result = doRequest(url, "");
+            String loginUrl = result.getString("login");
+            this.token = result.getJSONObject("poll").getString("token");
+            this.endpoint = result.getJSONObject("poll").getString("endpoint");
+            return loginUrl;
+        })
+                .subscribeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
+                .subscribe(
+                    result -> {
+                        Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(result));
+                        context.startActivity(browserIntent);
+                        poll();
+                    }, error -> {
+                        Log.e(TAG, Log.getStackTraceString(error));
+                        callback.onNextcloudAuthError(error.getLocalizedMessage());
+                    });
+    }
+
+    private void poll() {
+        pollDisposable = Observable.fromCallable(() -> doRequest(URI.create(endpoint).toURL(), "token=" + token))
+                .delay(1, TimeUnit.SECONDS)
+                .retry(60 * 10) // 10 minutes
+                .subscribeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
+                .subscribe(result -> {
+                    callback.onNextcloudAuthenticated(result.getString("server"),
+                            result.getString("loginName"), result.getString("appPassword"));
+                }, Throwable::printStackTrace);
+    }
+
+    public void cancel() {
+        if (startDisposable != null) {
+            startDisposable.dispose();
+        }
+        if (pollDisposable != null) {
+            pollDisposable.dispose();
+        }
+    }
+
+    private JSONObject doRequest(URL url, String bodyContent) throws IOException, JSONException {
+        RequestBody requestBody = RequestBody.create(
+                MediaType.get("application/x-www-form-urlencoded"), bodyContent);
+        Request request = new Request.Builder().url(url).method("POST", requestBody).build();
+        Response response = httpClient.newCall(request).execute();
+        if (response.code() != 200) {
+            throw new IOException("Return code " + response.code());
+        }
+        ResponseBody body = response.body();
+        return new JSONObject(body.string());
+    }
+
+    public interface AuthenticationCallback {
+        void onNextcloudAuthenticated(String server, String username, String password);
+
+        void onNextcloudAuthError(String errorMessage);
+    }
+}
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSyncService.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSyncService.java
new file mode 100644
index 000000000..647a9073c
--- /dev/null
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSyncService.java
@@ -0,0 +1,169 @@
+package de.danoeh.antennapod.net.sync.nextcloud;
+
+import de.danoeh.antennapod.net.sync.HostnameParser;
+import de.danoeh.antennapod.net.sync.gpoddernet.mapper.ResponseMapper;
+import de.danoeh.antennapod.net.sync.gpoddernet.model.GpodnetUploadChangesResponse;
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+import de.danoeh.antennapod.net.sync.model.EpisodeActionChanges;
+import de.danoeh.antennapod.net.sync.model.ISyncService;
+import de.danoeh.antennapod.net.sync.model.SubscriptionChanges;
+import de.danoeh.antennapod.net.sync.model.SyncServiceException;
+import de.danoeh.antennapod.net.sync.model.UploadChangesResponse;
+import okhttp3.Credentials;
+import okhttp3.HttpUrl;
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.RequestBody;
+import okhttp3.Response;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.util.HashMap;
+import java.util.List;
+
+public class NextcloudSyncService implements ISyncService {
+    private static final int UPLOAD_BULK_SIZE = 30;
+    private final OkHttpClient httpClient;
+    private final String baseScheme;
+    private final int basePort;
+    private final String baseHost;
+    private final String username;
+    private final String password;
+
+    public NextcloudSyncService(OkHttpClient httpClient, String baseHosturl,
+                          String username, String password)  {
+        this.httpClient = httpClient;
+        this.username = username;
+        this.password = password;
+        HostnameParser hostname = new HostnameParser(baseHosturl);
+        this.baseHost = hostname.host;
+        this.basePort = hostname.port;
+        this.baseScheme = hostname.scheme;
+    }
+
+    @Override
+    public void login() {
+    }
+
+    @Override
+    public SubscriptionChanges getSubscriptionChanges(long lastSync) throws SyncServiceException {
+        try {
+            HttpUrl.Builder url = makeUrl("/index.php/apps/gpoddersync/subscriptions");
+            url.addQueryParameter("since", "" + lastSync);
+            String responseString = performRequest(url, "GET", null);
+            JSONObject json = new JSONObject(responseString);
+            return ResponseMapper.readSubscriptionChangesFromJsonObject(json);
+        } catch (JSONException | MalformedURLException e) {
+            e.printStackTrace();
+            throw new SyncServiceException(e);
+        } catch (Exception e) {
+            e.printStackTrace();
+            throw new SyncServiceException(e);
+        }
+    }
+
+    @Override
+    public UploadChangesResponse uploadSubscriptionChanges(List<String> addedFeeds,
+                                                           List<String> removedFeeds)
+            throws NextcloudSynchronizationServiceException {
+        try {
+            HttpUrl.Builder url = makeUrl("/index.php/apps/gpoddersync/subscription_change/create");
+            final JSONObject requestObject = new JSONObject();
+            requestObject.put("add", new JSONArray(addedFeeds));
+            requestObject.put("remove", new JSONArray(removedFeeds));
+            RequestBody requestBody = RequestBody.create(
+                    MediaType.get("application/json"), requestObject.toString());
+            performRequest(url, "POST", requestBody);
+        } catch (Exception e) {
+            e.printStackTrace();
+            throw new NextcloudSynchronizationServiceException(e);
+        }
+
+        return new GpodnetUploadChangesResponse(System.currentTimeMillis() / 1000, new HashMap<>());
+    }
+
+    @Override
+    public EpisodeActionChanges getEpisodeActionChanges(long timestamp) throws SyncServiceException {
+        try {
+            HttpUrl.Builder uri = makeUrl("/index.php/apps/gpoddersync/episode_action");
+            uri.addQueryParameter("since", "" + timestamp);
+            String responseString = performRequest(uri, "GET", null);
+            JSONObject json = new JSONObject(responseString);
+            return ResponseMapper.readEpisodeActionsFromJsonObject(json);
+        } catch (JSONException | MalformedURLException e) {
+            e.printStackTrace();
+            throw new SyncServiceException(e);
+        } catch (Exception e) {
+            e.printStackTrace();
+            throw new SyncServiceException(e);
+        }
+    }
+
+    @Override
+    public UploadChangesResponse uploadEpisodeActions(List<EpisodeAction> queuedEpisodeActions)
+            throws NextcloudSynchronizationServiceException {
+        for (int i = 0; i < queuedEpisodeActions.size(); i += UPLOAD_BULK_SIZE) {
+            uploadEpisodeActionsPartial(queuedEpisodeActions,
+                    i, Math.min(queuedEpisodeActions.size(), i + UPLOAD_BULK_SIZE));
+        }
+        return new NextcloudGpodderEpisodeActionPostResponse(System.currentTimeMillis() / 1000);
+    }
+
+    private void uploadEpisodeActionsPartial(List<EpisodeAction> queuedEpisodeActions, int from, int to)
+            throws NextcloudSynchronizationServiceException {
+        try {
+            final JSONArray list = new JSONArray();
+            for (int i = from; i < to; i++) {
+                EpisodeAction episodeAction = queuedEpisodeActions.get(i);
+                JSONObject obj = episodeAction.writeToJsonObject();
+                if (obj != null) {
+                    list.put(obj);
+                }
+            }
+            HttpUrl.Builder url = makeUrl("/index.php/apps/gpoddersync/episode_action/create");
+            RequestBody requestBody = RequestBody.create(
+                    MediaType.get("application/json"), list.toString());
+            performRequest(url, "POST", requestBody);
+        } catch (Exception e) {
+            e.printStackTrace();
+            throw new NextcloudSynchronizationServiceException(e);
+        }
+    }
+
+    private String performRequest(HttpUrl.Builder url, String method, RequestBody body) throws IOException {
+        Request request = new Request.Builder()
+                .url(url.build())
+                .header("Authorization", Credentials.basic(username, password))
+                .header("Accept", "application/json")
+                .method(method, body)
+                .build();
+        Response response = httpClient.newCall(request).execute();
+        if (response.code() != 200) {
+            throw new IOException("Response code: " + response.code());
+        }
+        return response.body().string();
+    }
+
+    private HttpUrl.Builder makeUrl(String path) {
+        return new HttpUrl.Builder()
+                .scheme(baseScheme)
+                .host(baseHost)
+                .port(basePort)
+                .addPathSegments(path);
+    }
+
+    @Override
+    public void logout() {
+    }
+
+    private static class NextcloudGpodderEpisodeActionPostResponse extends UploadChangesResponse {
+        public NextcloudGpodderEpisodeActionPostResponse(long epochSecond) {
+            super(epochSecond);
+        }
+    }
+}
+
diff --git a/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSynchronizationServiceException.java b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSynchronizationServiceException.java
new file mode 100644
index 000000000..d907c229e
--- /dev/null
+++ b/net/sync/gpoddernet/src/main/java/de/danoeh/antennapod/net/sync/nextcloud/NextcloudSynchronizationServiceException.java
@@ -0,0 +1,9 @@
+package de.danoeh.antennapod.net.sync.nextcloud;
+
+import de.danoeh.antennapod.net.sync.model.SyncServiceException;
+
+public class NextcloudSynchronizationServiceException extends SyncServiceException {
+    public NextcloudSynchronizationServiceException(Throwable e) {
+        super(e);
+    }
+}